Here are my top 10 tips for photographing fireworks:
1) Arrive early to find a good spot.
2) Use a tripod and remote shutter release.
3) Use a small aperture between 4/5.6-f/16 (f/8 is usually good).
4) Use a slow shutter speed. Between 5 to 10 seconds works well. You can also use the bulb setting on your camera.
5) Set your ISO to around 100 or 200.
6) Make sure your flash is turned off.
7) Focus your lens ahead of time.
8) Take most of your photos at the beginning of the show. As it progresses there will be more smoke in the air and the sky won't look as clear.
9) Shoot wide. Make sure you have enough room in the frame to capture the entire display.
10) Be sure and take some test shots.