press x again after jumping, and if that doesn't work keep pressing x

Easy, just double tap X when falling and hold the X button on the second tap. You'll notice you become more 'floaty' as you fall after you've done this, a sign your chute has deployed :)

Just press the jump-button/key again when you're in the air. 
 
I guess the game manual could have told you that too. But those things are for douches!

"So yeah sometimes i see people dive off of tall buildings and manage to deploy a parachute or drop from heli's and do it but i cant figure it out i always just fall to my death when i try escape a exploding heli any clues on how to achieve these parachute falls ( Ps3 Controls Plz :D )   ta "

As has been said before, double tapping the X or A button depending on your console (PS3, 360) will open your parachute. Personally how I notice if my chute is open is by looking at my gun. If the gun moves up and you can see more of it, the chute is open. Also: if you're falling over water I don't think you need to open your chute, but I'm probably wrong with that thought.

Parachuting shouldn't be in this game. People just jump from choppers when they lose a little health instead of landing it and repairing it. Bad Company 1 had it better.

I wait until I'm pretty close to ground before I deploy my parachute or else you're just a floating target.

" i did have a quick look in the game manual didnt see anything in there about it maybe i missed or summat but i didnt see it in there, thx for replies "

It is quit hilarious watching the people drop from 3 feet and then deploying the parachute, because then the parachute stays deployed on them for another 5 seconds whilst they are running around.
Poor sods don't know they have given their position away.