In this bit I'll go over all the strats I've been using in my Old Patch runs
Most of this stuff should apply to the regular Any%

• Door doubletapping
  A tech used to open doors faster.
  When you doubletap a closed door with your Use key, it'll go straight to its closing animation and briefly become fully open in the process - you can go through faster as if youu only tapped once to open it.
  Useful in levels with doors that you want open faster like Deliver Us From Evil, The Family, The Last Piece or Judas.

• Door tripletapping
  An extension of the previous tech.
  After doubletapping a door and while you're going through it, you want to tap it one more time so that it ends up opening.
  Useful in levels with doors that you'll be going through multiple times like Initiation, Pawns or Traitor.

• Quick reload
  A tech which lets you instantly reload automatic guns.
  When using an automatic weapon (Uzi or Tommygun) you can switch weapons to quickly refill its clip.
  Useful in levels involving gunfights, which call for continuous fire, like Under The Radar, Straight to the Source or Rat Poison.

• Mid-air crouching
  A tech useful for reaching the ground faster.
  When you crouch, not only is the height of your character reduced, but your Y position is also shifted downwards.
  Useful for speeding up your descent in levels like Pawns.

• Neck snap delay
  Not really a tech, but an oddity of the game engine you should be aware of.
  When you snap someone's neck, their AI is active for a bit before they actually die (= are turned into a ragdoll). During that period, they can spot you and alert other NPCs in the level.
  Prominent appearances of this tech are in The Family, Amico Nostra or Judas.

• AI manipulation
  Tech which offers limited manipulation of the enemies.
  If you locate yourself in certain spots, enemies may have a harder time noticing you shoot/pull out guns.
  This can happen in the vent in Traitor, or on the railing inside the villa in Loose Ends.