Call of Duty: Modern Warfare 3 Tips

Ladder - Aim Time
Prior to climbing a ladder, press the melee button, and then begin to climb.
If timed correctly (for example the ladder on Seatown), the character will no longer need to bring out his gun and therefore upon reaching the top of the ladder, the gun will already be brought out ready to fire.

This can save time and may benefit in you getting a kill.