Scout
Power
Terminator
Armor
Some strategists proclaim, "The best defense is a strong offense." Obviously those people weren't being shot at. Since you will be shot at, you will want to be wearing at least some kind of armor. Space Marine armor is more than just a layer of ceramite worn over the body - it contains advanced and integrated technology such as communicators, life support systems, teleport beacons, and targetters.

No armor is impervious, and with a healthy dose of bad luck even the strongest of armor may fail to protect against the weakest of attacks. Therefore do your best to stay out of harm's way regardless of the amount of protection you have on.

It is important to study all types of armor, not just that which you are using, because it is unlikely you will be fighting against unarmored opponents. Learn to judge the armor penetration of your weapon against the thickness of your target, lest you find yourself watching your attacks ricochet harmlessly off your target.