Hi, I'm Blü!
I'm making this post to, in case you couldn't read the title somehow, give you my tips and thoughts on ''''''good'''''' level making! (I just want to quickly say that this will NOT make you instantly good or better right after reading this, as a lot of it boils down to training to be good at knowing what works the best for each part of a song.)
so let's not beat around the bullets and get right into the tips!

disclaimer: please remember that these are only my tips on level making and that it is thus completely understandable if you think that some of those are not good, and if you do think that, please tell me why, as I would love to see your view on those!

okay, this one isn't about level making itself, but it is part of it... somehow.
by simple names, I basically mean anything but this:
a better name would be:
(it's not the worst one I've seen, but it's the worst one in my list of level as of right now)

Q: but why would I care about this?
A: imagine you want to remove the xml of a level and his mp3 from your folder, if they have the same name, they'll be right next to each other, it makes it way easier, if it's different, it'll be nothing but annoying (also, your folder would look more organized, and that's always nice to see)

that way, you won't add stupid patterns and things just to have it be that difficulty you set, like 5... bubbles? pellets? who knows? not me that's for sure!
the level is easy and you wanted to do the hardest level ever? well what did you expect from making a level out of classical music?!?

This one is really important.
What I basically mean by this is to not add bubbles 'to make the level harder' (kinda goes with the previous tip)
I personally like to:

• use bullets on drum heavy part or to 'represent' a heavy/loud beat or when I want to fill/block parts of the arena
  
• use homing bullets on parts in the level where there's a stop in the song and I want the player to stay focused or when there's a high pitched sound/sound with an echo
  
• use bullets if none of those fits

Again, this kinda goes with tip #2, except that this time it's not about the difficulty, but the theme of the level.

Q: the theme? what do you mean by that?
A: Let me explain this by taking two default levels:

• Lost Age, a very calm and relaxing music
  
• Distant Stars, a really fast DnB song

the level for Lost Age is slow, smooth and focuses on beautiful patterns, and it works perfectly, because it fits the music in every way.
as for the level for Distant Stars, the level is fast paced the entire time, and would you look at that, it works perfectly yet again!

This one is by far the most important one of all, because this explains why your fast paced level feels weird:
it's because it doesn't fit mozard's Requiem in D minor.
(and yes, I know these exemple are extreme and won't ever happen, but I'm just trying to be as clear as possible)

yet another really important one.
Throwing a f*ckload of bullets toward the player out of nowhere without giving them a clue as to where they should go doesn't make the level hard, it just makes it incredibly frustrating.

Q: But then why do solvalou and nocturnal wanderings exist?
A: I remember bean saying on a stream that nocturnal wanderings was made because he wanted to see if people could do it... or something like that, all I remember is that he didn't beat it.

as for solvalou, it's just a bad level, and I honestly feel like all the thoughts on this level only went on the speech part (just because it's one of the default levels doesn't mean it's automatically good, and this one is one of the best example of this... and this is all my opinion!).

If you don't know what the spin rate of a level should look like, here's a trick: imitate body movement.
the best one is to move your head to the music.
no, I'm serious, it helps a lot.

when you move your head violently, you know you need to add a sudden quick spin rate, if you move your head left and right really slowly, it's probably a calm 'time to pull out the lighter and wave it around like gentle pyromaniac' song.
(which is also why I said 'imitate body movement' and not just 'imitate head movement', you could've listened to the music and though of people wave lighters around really slowly)

As for the time warps, it should be pretty easy, look at levels like 'I do, what I want.'
But, another thing that you can do with time warps is change the speed of the outer rings of the level, which is something I did at the end of my level Time

here's a shameless plug an exemple (the part I'm referencing is at 4:30) also note how the bullets shot at that part go against the tips I just wrote...

tweaks and tests everyday!
every 5 seconds tests and tweaks!
100 years testing and tweaking!
tweaksandtesteveryweeks.com
get the reference? if you did, good, if not, go watch rick and morty already!

when the player notices it, it can distract him from what's actualy going on (how much? depends on the person playing the level)

use the half-speed button to make sure it's right on-beat! (hell, I honestly think you should have it on all the time, it's that useful!)

do I need to explain why this is important?
...no, seriously, do I?

The latest update adds a new type of bullet: the hug bullet!
As someone who was in the beta to make a new level for S3, I was able to play with them in advance, and they're definitely interesting. However, finding an efficient use for them is fairly tough, so here's how I personally like to use them:

- To guide a player through a complicated pattern:
Could be useful when making basic version of hard levels. It kinda turns those levels into training levels for the hard one.
- To force the player to go through the hard path of a pattern:
Perfect to foul with the player by showing them both an easy and a hard path but only allowing them to go through the hard path.
- To force the player to go through a pattern instead of around it:
You can make player move around within a complicated pattern. I personally used this approach in my S3 level for example, I quite like this use for them.
- To make the player go through a pattern quickly:
Good example for this one: make a hard pattern at the beginning and let the player analyze it. Then near the end use it again and this time add a hug bullet at the other side. If they analyzed the pattern correctly, they'll know where to go to get through quickly.
- To recreate the ring level from Superman 64 in SD:
JK you're a ♥♥♥♥ if you do this one.

and I think that's all I have for now, so until then, have a good day and have fun making levels! :D