This is a dangerous level. No matter what you do, chances are you'll get killed at least twice. Of course, walking into the middle of the arena is suicide, as is walking around the arena. What's left? Sniping! Spawn at CP 4 as a sniper (remember that Empire sniper rifles only have one zoom level) and stand at the railing overlooking the arena. Be careful not to stand next to the turret or you might accidentally catch a face full of rocket. Fire across the arena at enemy units spawning at the other command post (2). Or, if you're up for a challenge, fire into the arena at enemy units. Don't worry if your reinforcements fall faster than your opponent's at first, you'll catch up.
Once the game has progressed a little (about halfway), you can leave your sniping position and either get into an AT-ST (1) or try to control the entire arena on foot with a grunt soldier. If you lose all of the arena CP's, you better get one back. Without one, all your efforts are wasted. Pick the method that best suits you, and don't get discouraged if you don't win this level the first time - it's harder than some of the ones after it.