Basically you need to pick up the drop shield from the dead spartan you first see. Use it when you health starts to get low. Remember to conserve you DMR ammo, use it only on the elites, after you break its shields. Try to pick up a plasma pistol asap, use it to mutilate the elites shields, then follow up with a DMR headshot. Don't be afraid of using the Needler (commonly dropped by grunts) after your DMR ammo runs out. Also make sure to use cover as frequently as possible, and only use the medipacks if your drop shield is recharging. If you survive over 40 minutes, you get a crapload of credits if you are playing with the "Free for all" setting. ~Happy hunting
