If I'm getting shot at from behind, I'll quickly turn the corner or jump off a ledge if possible. If I have the energy, I'll cloak immediately after doing so. Unless if the enemy has horrendous aim or connection, I'm pretty much a dead man if I can't do those two or if I turn around and fight. If the guy is shooting me from the side or front, I'll just armor up. I tend to use guns with higher rate of fire (or the amazing Grendel) so my chances of recovery are pretty good. Oh, and I have a habit of cloaking immediately after getting a kill because I hate getting shot at while reloading.