RBU is a weirdly funky game, with stupid physics and bizarre quirks. Here is a quick guide to the entire any% speedrun (specifically the tricks in it):

Level 1: A quick trick to go quicker is to start playing before you can see! Turns out, the splashscreen is delayed more than the code is, so you can get a small head-start because of this! Generally for the rest of this you just need clean movement, but with some keys, if you line yourself up properly with some keys, you can grab two in one jump, which is useful.

Level 2: This level is heavily based around the double key trick. Use it to go much quicker. As well as this, there is a key that, if not collected correctly, will drop you in a pit. Be quick when you reach it to bypass the pit. As well as this, this game has some (accidental) coyote time, so that allows you to collect the key needed after the pit key quicker.

Level 3: This level is the 'hardest' level. The first trick is just another coyote time trick, and then the second is to turn around when you get the key at the second box at the far left, then jump off of the small block to save about ~2-??? seconds (depending on the skeleton). The last is yet again just a key over a platform that disappears when you collect it, and you just need to jump when you get it to not fall in the pit.

Level 4: haha funny run to the end. That's it.

If you want visuals, take a peek at the current top Any% speedruns. Good luck if you have a go at it!