The most important thing to do when you're taking photos of the fireworks is...don't forget to watch the fireworks. Don't get so into taking the perfect photo that you forget to watch and listen to the music.
Everybody has mentioned that you should get a tripod or learn how be very, very steady without one. On occasion, I use a monopod. The last time, I had my monopod and my LCD screen positioned in such a way that all I had to do was snap the camera whenever I thought there would be a "explosion" of light. You have to sort of anticipate when it might occur because the camera will be slightly delayed when you take the photo. So...I watched and enjoyed the fireworks while my trigger finger kept hitting the shutter.
The first time I ever took fireworks photos (and videos of Fantasmic), I made the mistake of putting the camera on auto-focus. Take that off if you can and set the camera to focus on infinity.
The photo below is actually from
Disneyland and was taken while sitting very, very still in front of the castle. I didn't have my monopod with me. I like my monopod but I'm actually in the market right now for a smallish tripod for December's trip.