Objective 1: Infiltrate Compound
Run to the main gate, you can climb the fence on the left part of the gate but before that check the patrolling guard and when straying to your left sneak closely and shoot him once in the head with your SOCOM. Climb the fence and crouch your way to the truck near the helipad.
Objective 2: Sabotage Radio
I just hope you still have some ammo left for your sniper rifle... I have one left myself. If you don't have any ammo or if you brought the wrong gun (AK47?! who told you to bring that?!) then head to the guard house at the main gate, there's a rifle inside along with two guards as well. Snipe the guy standing at the radio tower, there are 3 guards patrolling around the house and they also get inside so better enter while they're out. Head up and sabotage the radio. Climb down the stairs and wait for one of the 3 guards to stop below the tower. Snap his neck from behind, head to the guard at the kitchen and snap his neck too. You probably noticed a computer on the other room, use it to disable the security cameras for 2 minutes. Never mind the guard inside the comfort room and go out.
Objective 3: Acquire Ammunition For Helicopter's Gun
Use the backdoor of the southern warehouse, if you disabled the security system on objective 2 then just get in... if not then just shoot it before it sounds the alarm. Enter the warehouse (still crouching of course) and jump to the crates on your right. This will take you up to your chopper's ammunition and some ammo for your SOCOM, proximity mines and other guns as well. Head back down the and leave the same way you got in.
Objective 4: Power Up Fuel Pumps
Run around left of the helipad and to the fuel pumps. Shoot the guard while his standing at the front gate, shoot the other guard inside and then the camera. Activate the panel to open the gate and power up the fuel pumps.
Objective 5: Activate The Fuel Pump
Activate the fuel pump and wait for less than 3 minutes. Anya will report that 2 enemy helicopters are going to your location so better get some place to hide. You can hide inside the guard house near the fuel pumps so you can activate it again in case an enemy turns it off. If in case an enemy enters your hiding place, just shoot with your SOCOM.
*** A BETTER(?) SUGGESTION ***
After objective 2 do objectives 4 and 5. This way the enemy will approach the compound while your heading to the warehouse for the ammo. You don't have to wait and hide to a place nearby for almost 3 minutes, besides this is a big building and you can hide behind the crates on the upper section. You won't be noticed and in my experience in this mission if you hide at the warehouse enemies outside will not turn the fuel pumps off.