Whenever you start a mission try your best stealth against your enemies, that way you can save more ammo and more score at the end (x8000 score for each stealth kill). Also when you get hurt don't use armor until your health is about 1/2 way empty or lower so you don't waste any armor.

To defeate jaws, make him throw gas tanks and bring him one by one blow up the gas tanks.

When you're on the highway drive on the line that seperates each lane.
It works great!

Just a little heads up, if your trying to get the cheats to work like double ammo or all weapons you need to get ALOT of platnim on the levels.

Meaning you need to unlock them first!

When you start the mission and are going to get the car, turn to your right instead of left into the door at the end of the catwalk Turn left there and you will find a black motorbike.