From Halopedia, the Halo wiki
You begin in a rather good position, overlooking several structures patrolled by Crawlers with Watcher overwatch. Begin your assault by picking off every enemy you can from afar with whatever ranged weapon you have. Pay special attention to the Crawler Snipers on the ridges...getting pegged by a Binary Rifle shot is extremely annoying early in the mission.
Once you've eliminated every enemy you can, move to the first way point and deactivate the COM scrambler there. With that done, the communications between units will clear, and you can move ahead again. The rest of the mission is pretty easy. Simply follow the waypoints, killing any enemies that get in your way (keep your eyes up, Watchers can warp in from the sky pretty much anywhere they want to) until its time for extraction. THAT is when things get hairy. A small army of Crawlers shows up and rushes you. Thankfully, your dropped Rocket Launchers. USE THEM LIBERALLY.
Once the last Crawler comes apart, run to the descending Pelican and your done.