Feel free to add more in the comments, but here's some current tech being used that you might not find from just playing the game.

Grenade/Explosion Boosting: This one is really basic, but runs have been submitted without them. Use the shotgun alt fire on the ground to move fast. Usually you look down while moving forward and it will boost you forward and very slightly up. Also you can use a grenade on a piece of glass above you when you're contacting it/near contacting it and it will break the glass and boost you upwards. There's also the full pump charge/ shotgun explosion boosts faster and can be used mid air, but does more damage. Generally, explosion boosts will move you towards where your camera is pointing if grounded and opposite the camera if airborne or something is in front of you. This trick is ubiquitous, you will see it in basically every level. The Blue does 35 damage, Green does 50, and you have 100 health, so you only get 2 blue, 1 green, or 1 green and 1 blue per checkpoint unless you damage an enemy.

Slam Jump: Do a midair slam, then immediately jump. Gives decent height without having to lose health from an explosion boost. Used most notably in 0-4 to skip the final arena trigger. The downside is it's not the fastest form of movement, but it costs no health and is quicker to perform than slam storage and more useful in lower ceiling rooms.

Slam Storage: Do an air slam and a wall jump at the same time, and as soon as you hit the ground, do a normal jump and you jump very high and fast. It's used most notably in 0-3 for the developer intended skip straight to the boss. It's faster than grenade boosts, but only goes straight up unless you combo with whatever air strafing or shotgun explosion boost you combo with it. it can also be combined with a slide to move quickly horizontally.

Bunny Hopping: Since the new patch, you can conserve momentum by doing more slide jumps when you hit the ground in a small window. Used most notably in the Chapter 2 boss hallways. It can be chained with most other forms of horizontal movement.

bhopping is easier if you slide after the dash jump. i've noticed it gives a bigger window and still conserves momentum, so you can have 3 bars of stamina while going at full speed

ok so I checked via mods and as it turns out a dash jump is at about 49 velocity, a grenade jump is at 70 or so when sliding before it, and an ULTRABOOST is at 140. Note that the max. slide hopping speed is also at around 70 or so.

also* max slide speed (and therefore, afaik, slide hop speed) is capped at 3x the default slide speed, whatever that is