-"First shot, Second shot, Last shot". This is a classic sniper technique that will save your ass one day in the field. Take your three shots then relocate.
-"What you think is a good hide, isn't". Avoid fallen logs, and shooting from trees. The exposure off the side of top of your cover is only an odd shape to the human eyes. This is called "Tree Cancer". Cliche hides are nothing but a dead giveaway to a trained Countersniper.
-"Guerrilla Warfare". Read every article you can find about it, because it just may be a good friend.
-"Spotters". Are unnecessary in Airsoft, they are just another person to give away your position.
-"Play it smart". Make sure you don't lose sight of your enemy and get yourself surrounded, always keep to the outside of firezones for a far flank, your long range will come in handy.
I myself use spotters more like a handy two legged back up/close range life savers. =D Covering up me rear etc... Propably Finnish dence woods as an playing area (from like 9 out of 10 playing areas) has its effects.