Ive seen many people out there on public servers, that don't know how to climb a ladder fast, instead of the normal.
What you got to do is:
When attaching yourself to the ladder ( walking/jumping into it), you gotta look sideways up, whilst pressing the your up key, and your side key(depends on which side you are looking).
This will boost your climbing x2, So you'll get much faster up, and can easily take out your enemy.
Also, the box jumping.
This you have got to use when you want to jump on a box, you normally cant jump on.
Look into the box you want on whilst walking into it. Keep walking, press your sit-key, your jump-key, and your sit-key again.
This will allow you to jump much higher, whilst your char's feets are also going up in the air.
Good killing out there.