In the level "Going Hunting", you take control of the co-pilot of an F-18 Hornet tasked with shooting down enemy planes. To get the 'You Can Be My Wingman Anytime' achievement, you'll need a perfect playthrough of the level. That means you don't get hit, and all the enemy planes are shot down without running out of ammo. Do this, and you'll get 30G on Xbox 360, or a bronze trophy on PlayStation 3. If you need some guidance, check out the video below.
Having not put in enough time with Battlefield 3 yet, I really want to power through the rest of the single player now. Maybe I'll get around to it after sinking more time into Skyrim, Modern Warfare 3, and Rayman Origins.