Lead Baloon pretty much has it. Try to get a shot head on (at an angle of course slightly to the side) coming at you. You are looking for a 3/4 shot. It will give the camera the best chance to capture a good shot. If possoble try to manually focus. Pick a spot and pre-focus. Have the plane fly through the area. When it is there take the shot. Also Pheonix (I believe it is Pheonix optical) makes screw on lenses. They screw on the threads on your lens. Some cameras do some do not. Usually the higer end stuff has them. You can get telephoto adapters. I am not sure of the model you have. I am a film guy. Can't afford a digital SLR yet. As stated try to set your ISO speed as high as possible. 400 minimum, 800 if possible. This will give the best (highest) shutter speed and get a non-blurred image. Good luck and have fun. Any real bad shots can just be dumped so shoot as much as you can.

Mark Shuman