Search and destroy: When you have the airstrike don't use it straight away, maybe not even use it the next round (As people will know you have one and will more than likely run into a building.)
Team deathmatch etc: Wait for a UAV come in, if you see a blodge of people, place it there.
do you mean at what direction the planes drop the bombs?
If so then you cannot control the direction the planes come from.. there is a myth that if you drag the analog stick toward the direction that you want the airstrike to hit that it will actually do it but I doubt it.
If you can see where they are, Just look from where you are from them and they should be moving towards you so move it somewhere inbetween you both on a path.