I'll copy paste this stuff into me guide but I'll post here just so you can keep your lazy fingers on this page.
Here goes... something:
Grenade Momentum- While running throw a grenade. This'll make the grenade go farther at longer distances. Also works great while jumping.
Spray- Meh, too basic. Figure it out. Other than that used for lucky kills offscreen.
Aim for the chest- With an automatic weapon, try to aim for the enemies chest for full fire coverage.
Crouch Midair- Crouch midair while the enemy is in horizontal sight of you so that its bullets well hit less often. Also with Barret, you can snipe far distance with it without big recoil.
Clicking Happy- Preferably with AK-74 or FN Minimi and with a map that has decent amount of jet fuel, keep on clicking both buttons at the same time. Works wonders.
Stay above your enemy- Try to stay above your enemy all the time for easier shots and headshots.
180 Degree Spray- With an automatic weapon, rush at an enemy camping near some type of block (Like sandbags, boxes, stuff) and jump over him while spraying the area. Risky.
Nade Jumping- When a map has a low amount of jet fuel or none at all, throw a nade near you and jump after counting about 3 seconds. This'll give you a considerable boost.
Knife Throwing- Throw your knife using weapon throw button (Default F). The longer you press the longer you throw.
Chainsaw Massacre- Charge at your enemy while in crouch position midair and use the jet until you reach the target. Deemed near impossible.
Burst Midair- Again, use either AK-74 or FN Minimi and instaed of single shots, burst while rapidly tapping jet button.
Headshots- Aim for head. Harder than you think.
Ricochet Nade- Throw a nade against a wall and hope it ricochets to the other side when normal throwing won't work.
(Note: Very risky, dangerous, and goddamn hard to pull off)
Back Hit/Stab- Go behind an enemy, hit him once, run back, and fire at the unarmed asswipe.
LAW Launch- You're more likely to kill yourself then to successfully perform it. Jump and crouch while in midair, take out your M7 LAW, and shoot it on the ground to cruise across the screen. Even then, surfing the skies into enemy territory is still freaking dangerous.
Randomness- When an ammo of your weapon runs out while in a middle of a firefight, pick up a weapon from dead enemy and use that weapon against your enemy. Side-effects include weapons disappearing miraculously, taking longer to find the weapon then reload, and getting a crappy ass weapon that you'd not call it a weapon.
Rush- Go infiltrate the enemy lines ASAP and shoot them in the back. Make sure the shots are 100% accurate.
I know I missed some so I'll post some more when I want to. Giving your own techniques will contribute to teh guide and maybe with your name on it.
...Fine your name will be on it. Just don't rampage me with your new learned skills