Halo 3: An effective method for taking down brutes is to hit them with a charged plasma pistol shot, then melee them in the face right after. if you can't get close enough, consider dual wielding both a plasma pistol and a magnum, and follow up the charged shot with a headshot. Against the flood, always trust in the dual plasma rifles, and if you know the weak spot, the battle rifle is also incredibly effective. The Assault rifle, on the other hand, is almost entirely useless. Those tactics got me through the game on Heroic, it'll do for you too.