If you want sharp shots try a shutter speed of 500 or better. the slower shutter speed the better chance of getting some blur in the shot. If you pan you can get a sharp shot with a blurred background. Shoot lots and experiment with the settings.
Fast shutter speed and/or panning the camera with the subject; depending upon the effect you want to achieve. Typically, it's a fast shutter speed to stop the action.
If you're flying in a small airplane, and you see another airplane outside the windshield, and if that airplane does not seem to moving, but just getting bigger you won't have to worry too much longer about how to take pictures of it.