Pretty much just go through the missions: (On Veteren difficulty)
Persona Non Grata
Back on the Grid.
Now a tip for the Back on the Grid mission when you have to sit in the turret on the technical I kept getting killed on it so I figured just as you get off the little shack with the ladders, just sit in the corner once you drop down its easier to let Price and Soap (Or of course yourself) shoot the enemies without dying in the turret, once the mortars come in just sprint towards the objective marker. Trust me this is much easier than dying a hundred times in a trucks turret. Happy hunting : )