All Gun:

While playing walk foward once [ hold shift and press up ]Then walk backwards once [ hold shift and press down] hold right utill she does a 1080 [ 3 turns ] then do a backflip. you will hear a click if you have done this code right.

Skip level:

do the same as the all guns code exept for jump foward instead of doing a backflip

To get all weapons and ammo:

Walk one step forward
Walk one step back
Turn round three times in any direction
Jump backwards

To skip to the next level:

Walk one step forward
Walk one step back
Turn round three times in any direction
Jump forward

It's a bit easier to use these cheats if make Lara walk while you're trying them.

Tips:

To ride on a raptor or a t-rex at the lost valley, just shoot the dinosaur 2 times with your shotgun and turn around and do a backflip to ride on it(this cheat needs a lot of practise to succeed so just be patient if it doesn't work)