Campaign Mode: Single Player
On easy, just charge in with some strong weapon combo (SMG and Plasma Rifle) and slaughter everything in you path. Same with normal.
On Heroic and Legendary, duck and hide A LOT! Never go charging anywhere! If you charge into 2 elites, most of the time, you’re dead. Hit and run is what you should do. Take snipes, and use active camouflage all the time if you’re the Arbiter.
Don’t bother with close range weapons on legendary or heroic.
Use grenades to flush enemies out.
On legendary, sometimes, you can get in a fast vehicle and try to run through the whole level. ALWAYS have good weapon combos.