To sum what everybody said.
Move frequently, quickly, and with great stealth.
Take shots that you know you can make, from angles that give you the advantage.
Use Camo to you advantage, stay concealed.
Try to engage on your terms.
Get the proper kit (knee pads made a huge change in my play style)
Be able to shoot with your left and you right hand (super important)
Have buddies that you communicate well with (I usually role small in a group of three, but I move a lot)
I don't think anybody has said this but: PLAY AS MUCH AS YOU CAN
I have a buddy who shoots a 15 dollar spyder clone and plays every week. With in 2 months has was one of the best players on the field. Practice is essential!
Oh and remember to have fun, sometimes bum rushing the enemy is the best choice
Good luck, gog some guys!