Two comprehensive guides on nekodancer are provided here and here.

BUT WHAT HASN'T BEEN MENTIONED YET??

The ratings for notes in tier order are:

It is important to take into account that the notes are perfect 44x44 px squares. You may have already figured this out from the rotate powerup, before it was converted into wind. This means that the hitbox for achieving the specific note ratings will be exactly the same for every kind of note. To be more specific:

Don't be afraid if it seems small: This is only an approximation, and the notes move slow enough for you to be able to land this small gap (it's actually displaced upwards slightly, so be proactive about hitting notes).

The next question:
Just how costly is a miss or oops when you are maintaining a big combo??
Through some calculation, if a mistake is made during a combo exceeding 30, you will actually lose a minimum of 60 points, excluding the penalty for an oops or miss. This is why you cannot afford to make major misses in the middle of big combos, especially with an opponent chasing you closely. The general principle: It is better to make a mistake near the beginning or the end, rather than in the middle.

How do you know if you are performing well??
There is actually a little constant you can extract from your score to indicate how well you have performed. GIVEN you have achieved 100%, you can multiply the total number of notes by 10 and then subtract it off your score to leave this special constant. Now look at this list: How well have you performed??

<-200: You've got a lot of work to do.
-200 to -100: This was probably a hard song, keep trying.
-100 to 0: Not too shabby.
0 to 50: Pretty good, you went positive.
50 to 100: A good run.
100 to 150: An excellent run. You'll be firsting frequently.
150 to 200: Right up top with the pros.
200+: Rare and the mark of a real pro.

NOTE: Not all songs will provide this constant above 200, but most will do above 100.

Nekodancer's tracks work off the pulsation patterns off songs. Here is an example of what a pulsation pattern looks like:

Nekodancer's generator is more likely to generate more notes if the pulsation patterns are further apart and more defined. The maximum frequency of notes is 280 pulsations per second. Here is what the pulsation pattern of the infamous song, 280 bpm, looks like:

Another well known song: This is the pulsation pattern for the fast part in sporty-o's "Let Me Hit It" (audiostalkers remix)

Easy songs
You should ALWAYS begin at the basics. You should pick the easiest possible songs. Some good songs are ones with pulsation patterns spread distinctly and as far apart as possible, with little to no breather spots (we will cover this soon).

There is a thread on the forums that shows a list of some songs from easy to extreme difficulty. Start from easy, and then move up a tier once you feel comfortable. Click here to see this thread.

This is the pulsation pattern for Eric Prydz - Call on Me. It is extremely simple and is perfectly in sync, so I recommend something like this to boost your confidence.

Relaxed hands
You should always have totally relaxed hands while playing. There is no reason to hit a note hard at all, because it's not going to make getting perfects any easier. There are times where you will have to make quicker jabs at the keys for precision, but you should be moving your wrist, not your entire arm.

Try comparing this motion to any musical instrument you play, if you do, and just try to have that same level of relaxation. I play a violin, so personally it's easier for me, as hand motion is extremely important.

To show you an example of a relaxed hand, I actually recorded a fingercam of 280 bpm. Note how my hand is completely relaxed throughout the entire song, and it never tenses up unless I make a mistake.

In addition, you should NEVER gear up for a note after a freestyle (you shouldn't suddenly ready your hand either). It may force you to subconsciously adjust your hand position, making it very awkward to adjust back to the style of play you were rolling with before the freestyle. Thus, it is more likely you will make a mistake. When preparing for a note, you should look at the next series of notes, in case you are hit with a powerup, so that you will be prepared to know what comes next. You should apply only a small amount of pressure to the note you are about to press, not change your hand position entirely. The video shows a good example of this.
Gaps
A gap is a section in the song where the pulsation pattern becomes inconsistent, and the notes are spread apart further than normal, causing an inconsistent section in the song. It is important to note these inconsistencies for fast songs, in order to earn 100% and perfects on every note. Not only that, being aware of these inconsistencies in the songs gives you a "micro break" - a microscopic period of rest, in which your mind refocuses itself on the notes coming at you. It is similar to taking a breather during a high-intensity workout: your body can't exert itself continuously for long periods of time.

There are 2 gaps in the fast part of sporty-o's "Let Me Hit it" (audiostalkers remix). You can see them below when the pulsations contract slightly.

An example of a gap in Disco King: Do you see it?

If you didn't see it, it is right where Ciliskee's name is. If you still don't understand, those two are the only adjacent notes whose sprites do not cross any common y coordinate on the image.
Panic attacks
In what situations would you just lose your sense of control, and panic?

You would suddenly cease to function properly if you were hit with two powerups suddenly, such as speed and blink, without any warning. In addition, you can also lose control if you are paying attention to the spinning star showing your massive combo - the higher the combo, the more likely it will throw you off.

How can we deal with this??

You should be totally prepared for at least 3 notes, but no more than 5 notes, after a freestyle has ended. This will stop you from suddenly panicking if two people hit you with powerups out of nowhere. However, you should not expect a powerup to always come up, as this can force you to tense up and lose control. Again, you should be prepared for the notes, but apply some slight pressure to the first note coming up. You can then time the other notes by memory. Should the order of the notes be committed to your mind to such an extent that it doesn't make you tense up, the input should be totally automatic and smooth.

You should also occupy yourself during a freestyle. This can be done by participating in the freestyle: There's no problem with goofing off, or checking if your keys work. But you should be paying attention to the arrows. You don't want to be caught goofing off just as the freestyle ends. You can send a message or two to your friends too: get your mind relaxed! :) you should be enjoying yourself and having fun, instead of being serious about it. Don't look at the spinning combo star, and try not to glance at the leaderboard too much. One peek is enough.

When playing through a song, you should not be glancing at the leaderboard at all. It is a huge distraction if you are coming short of your expectations in the middle of a song, and it interferes with your confidence.

Again, DO NOT PAY ATTENTION TO THE COMBO STAR, OR YOUR PERCENTAGE. It can force you to become overly excited, or even afraid about missing the next note, and is a MAJOR distraction. Don't be tempted by arrogance!! (Too true for me)
Take a break
This is VERY important, for your performance in this game and for your health. You should be taking care of yourself. Get plenty of sleep, and eat properly!!

The human body has a maximum attention span of 90 minutes. You should be taking breaks every 90 minutes, AT MAXIMUM. You can take this opportunity to drink some water, or have a nap, or just pay attention to something different. Chat to your friends. Do something that involves you not having to do anything physically.
YOU SHOULD NOT BE PUSHING YOUR LIMITS. Everyone has their own limits, no matter how strong they are. TAKE A BREAK. The moment you start screwing up because you're tired, the more frustrated and unconfident you'll become, and the more likely you're just going to spiral into an increasing mess of frustration and anger, and possibly physical pain.
How to approach each note
You should focus on a particular region of the screen, while there are notes playing. You should not be scrolling your eyes upwards unless there is a long break between notes. As a general rule, the more densely packed the song is, the further down you should be focusing, and the more tight the region of focus should be. You should not be keeping your focus constantly on that particular region though, as it will diminish your physical strength more quickly than taking breaks throughout the song and finding opportunities to loosen off, and just have fun.

More strategies to approaching each note will be covered in the always perfect section.
Two handed techniques
The spread technique: Left hand on A and S (Left and Down), and Right hand on Up and Right. This way you can see each note as being in a row rather than corresponding to a particular arrow, and you can ignore the orientation of the arrows: all you have to focus on is which column they are in.

Speed
VIDEO DEMONSTRATION
Credit Anthonyjones for this video.

The common misunderstanding players have with this particular power up is that it gives off the illusion that there are more notes coming in higher densities. This is incorrect.
You should simply relax, and understand that the notes are actually coming at you in the same speed, but are just moving faster. In addition, since the notes are moving faster, you will be able to see more clearly the exact locations in order to hit perfects, so try to take advantage of this power up instead of fearing it.
Another trippy spot with this power up is the moment it ends. To overcome this, try to keep your mind set on hitting the notes in time with the music if you can, rather than using your eye to focus on the notes. Memorisation of the positioning and timing of each note can also help.

Rotate/Wind
VIDEO DEMONSTRATION
Credit Anthonyjones for this video.

This is a rather tricky power up. The notes will go off to one side and appear out the other, and fall towards your arrows in a diagonal pattern.
The way to deal with this power up is to watch the note's vertical movement, rather than focusing on the horizontal. Use the horizontal motion to tell you which note to press.

Blink
VIDEO DEMONSTRATION
Credit Anthonyjones for this video.

This powerup can be a real disaster, when high densities of notes are coming at you.
The important thing to remember if this happens is to never guess. Make sure you are absolutely certain where a note is before you attempt to hit it. Try to focus your eyes a little higher away from your arrows if you can. This way, you will have just a little more time to see where a note is before you hit it.
Memorise the movement speed of each note in order to get perfects.

Short
VIDEO DEMONSTRATION
Credit Anthonyjones for this video.

All this does is shorten your vision above. The important thing to note is that there is a purple image showing you the areas that are blacked out. Make sure you are focusing as much as you can on the track, so that you don't get caught off guard.
If you are in a short power at the end of the freestyle, you can see where the freestyle ends on the progression bar (rainbow color), or you can see the end of the freestyle bar coming down the side of the purple screen.

Wave
VIDEO DEMONSTRATION
Credit Anthonyjones for this video.

This has a similar effect to wind, but it can throw you off because it's confusing to tell which note is which.
However, the notes don't waver too much, so if you focus you will see which note to hit. Pay particular attention to the orientation of the note.
There is a catch to this power, unlike wind. The notes in wave will actually not stop on top of your arrows, but rather off to the side. This can throw off your momentum if you are too focused on waiting for the note to overlap your arrow completely.
Again, follow the vertical movement of each note, and make sure it corresponds to the vertical coordinates of your arrows. Do not pay attention to the horizontal movement of the notes.

Want to be able to do this all the time?



Let's make it happen.


Understanding the Game
Recall this?

This is the approximate hitbox area for each arrow. You should practice on several different types of songs (fast and slow) in order to get a feel for where the best place to hit perfects actually is. Since there is a delay between pressing down the key on your keyboard and the input registering (almost microscopic lengths of time), the actual feel of each perfect indicates the best place to go for each perfect is actually slightly above the note, rather than exactly on center. Give it a try for yourself - maybe you prefer a spot-on approach to each note. But just remember that there is a very small amount of space for a perfect, and it is NOT PIXEL PERFECT. (It DOES change to become pixel perfect sometimes -- nekodancer is not entirely consistent)
Playing Techniques
There are three different techniques, based on three parts of your body: Your eyes, ears, and hands.

By Eye and Ear

This strategy uses the ratings on notes as a guide. The eye is used to identify whether the hand is moving too fast or too slowly (for example, I start getting a lot of nices all of a sudden progressing towards okay, then I obviously need to speed up or slow down)
The best place to use this strategy is in songs with fast parts (notes coming at a constant but fast rate). For example, Kick Drum Metronomes - 280bpm.
CONS: Requires large amount of concentration and can strain the eyes. When going through a song with a breather spot, the eye can mistake this as an opportunity to switch over to the by-eye-and-hand strategy. Then, the beat will go back to normal and you will be forced back to the by-eye-and-ear strategy too quickly, causing you to panic, lose your momentum, and score a lot of nices and okays at once.
By Eye and Hand

This strategy uses the note positioning as a guide. The eye is used for all forms of timing within the song. (for example, at the end of freestyles, I will be absolutely certain to at least get a perfect on the first note if I know exactly where to hit it)
The best place to use this is in slower songs, or slower parts of fast songs. The eye will have a lot more time to react to each coming note, unlike the by-eye-and-ear strategy, in which the eye just tells the hand whether to slow down or go faster. Instead, the eye will tell the hand WHEN to press each note, rather than HOW FAST to press each note. This strategy is the best for identifying breather spots. It is also great for songs which have no evident beat. This technique is best for gaining frequent perfects.
CONS: Fails on fast songs due to high concentration. Fails in the long term due to fatigue. Put under stress in situations where the player is constantly being hit by powerups from other players.
By Ear and Hand

This strategy uses the beat of the music as a guide. This time, the ear is used to tell the hand when to press notes, and also how fast to press them. (For example, an on sync song with a constant beat is a great way to score perfects using the beat of the music)
The best place to use this is on songs with zero breathers, or with songs that have short segments of fast notes. (For example, Savant - Wildstyle, or songs with one single note used multiple times in a row). This technique is useful for maintaining a constant rhythm with the fingers -- not moving too fast or slow.
CONS: Fails on breather sections, because the gaps between notes are totally ignored. This can result in many nices or okays which seem inexplicable. In addition, the body can think it recognises the gap of two notes subconsciously as being equivalent to one beat in the song, and it can result in an Oops, destroying your combo.
Confidence Building
Here is a list of what you should do to build confidence. You cannot get perfects constantly unless you are confident in yourself!!

• Play more songs, and 100% as many as you can. The more you 100% each song, the more comfortable you'll feel about achieving high scores, and the less the influence of other players following behind you will be.
• Watch others play. There are some videos on YouTube of other players playing Nekodancer. I myself have some videos (some of 100% in hard songs). If you have trouble keeping up, try to slow down and identify the patterns made by successive notes. Then, try to practice these patterns by yourself. It will not only give you confidence that you can actually do it, but will give you practice if the pattern turns up in the future!!
• Talk to other people. You cannot be confident in yourself, and you cannot be powerful if nobody believes in you. You need to make friends - this is not a one player game. "A God does not have influence over the world if nobody believes in him." Personally, I would be crushed if people stopped believing in my abilities. I don't want recognition - I just want support, and there is definitely a distinction between those two morals. I have met several amazing people on here, including the others people hail as the pros of this game, and I would be devastated if I ever had to go through this game without them supporting me, as it is what has taken me this far. Anyone reading this can come talk to me if they wish - I will listen to ANYTHING you have to say.
• Play on slower songs. I have already mentioned this earlier in the guide. Don't frustrate yourself over hard songs. Going hard is a great thing for improvement, but you do have your limits. You might find that as soon you start a slower song, you'll have a much smaller occurrence of perfects. Just take it slowly, and try to find the right place to hit perfects. Soon you'll be back on your feet in no time.