Some tactics i found helpful in the MP
1)Always try to keep cloaked as long as possible. Manage your energy so that you still have about half the energy to use
2)When ever you find a foe and you are in cloaked mode, don't just go firing! You'll just lose all your energy and you might get killed instead of killing.
3)So, move in cloak, find a foe and when ready to engage switch to armor and kill that sucker.
4)Don't camp in clocked mode. You can't be seen i know, but your shadow can be seen. And you might even run outta energy before you even know it
5)So if you see an shadow near a wall and no person, question yourself later, just shoot.