1. A well placed grenade and couple shots to the head with the Battle Rifle usually is very effective
2. When using dual plasma rifles pull on the trigger twice before holding, shoots faster then move in with a meelee to the head, man drops dead.
3. a timed move to the side will avoid being slashed to death with the covenant sword, timing is key.
4. Using the Shotgun, if you are not too close but running up to him, fire a shot to the head and then meelee, he will drop like a fly.