This sort of continues what crobodile was saying:

Fast Jump glitch: If you do a dive jump, you can push jump on the same frame you land and keep all of your momentum. This is very inconsistent though, and the best way i have found to do it is to mash the jump button before you land. This glitch is super useful on levels with long, flat surfaces, and is the fastest way i know of to move normally.

Level 30 clip: This is by far the hardest glitch (besides some crazy TAS stuff) in the game. Basically, you can use the moving platform at the start of level 30 to clip out of the starting room. In order to do it, walk off of the platform and turn around right before it hits the wall. If you are (extremely) lucky, then you will clip out. It is very inconsistent though, sometimes clipping you into the wall (good luck), and sometimes clipping you all the way through the wall (bad luck). From there, you can wall clip to the platform above the spawn, do a super jump on the farthest right corner, wall clip off of practically nothing, and somehow get into the death zone without dying, in order to save a lot of time. (I'll put a video once i get the chance)

Weird ceiling clip (level 24): On level 24, you can do a precise dive to clip all the way through the ground. This is inconsistent, but it can save a decent amount of time. Do it coming into the main area from the coin area.