Freeze the Action
Here come the airplanes--how do you get good, sharp, interesting photos? First and foremost, you want to freeze the action. That requires a fast shutter speed and the ability to pan along with the plane's motion.
To get a fast shutter speed, I recommend that you use your camera's aperture or shutter priority mode, not automatic or program mode. Dial in shutter priority and, with the camera pointed up to the sky, dial in the fastest shutter speed you can. Or, in aperture priority, choose the smallest f/stop number possible, which will give you a fast shutter speed. Whichever way you do it, your shutter speed should be at least twice your focal length. So if you're using a 200mm lens, you should be shooting at 1/400 second or faster. That's really just a rule of thumb, not a mathematical principle, but if you're shooting a 200mm lens at 1/60 second, I guarantee you'll have a blurry photo. I took this photo with a 400mm lens and a shutter speed of 1/800 second. If you have trouble reaching a fast shutter speed, increase the ISO a little to make the camera more sensitive to light.