Plant claymores in prototype factory when you capture it. If you know the spots, you can plant them so they go off before the enemy even sees it. When attacking the prototype factory, bring grenades. They are very useful for stemming defensive action by the enemy and blowing up claymores. There is a shopping cart sign at the bottom left corner of your screen. If this turns into a flashing flag, someone is in the same territory as you.
Never cloak at close range, as people can pinpoint your location by sound.
Use radar scanners whenever possible, as they are extremely useful as Intel for close by friendlies as well.
Always use a laser on automatic weapons. This reduces the spread and increases accuracy.
When sniping, find a good spot on a hill, cloak. Then when you find someone, go into strength mode (reduces sway) and go for the headshot. Once you make your kill, get out of there. The sniper has a loud distinct sound that gives away your position, and a big muzzle flash as well. So once you make your kill, move to a different spot or lie low for a minute to get rid of impatient enemies trying to counter snipe you.
That's it for now. =)