Small timesave in the opening by skipping a switch to get blue key.

The narrow hallway to red key can be really bad. I try to kill as many enemies as I can on the way there so there's less blocking you on the way back.

There's 2 jumps towards the end you can do where one skips a staircase and the other an elevator. Found the elevator skip jump too difficult and skipped the other jump to grab health instead.