Fireworks are fun to shoot, I'm sure there's a better way but here's how i got a few:
• get a good location for composition
• tripod and remote trigger are a must
• use a wider angle lens
• Bring a piece of black cloth or something completely light restrictive that you can quickly cover the lens (without disturbing the camera)
• take a few test shots of your area, and try to stay downwind (away from the smoke)
• I used bulb mode, and incrementally stepped the exposure/iso until i liked what was coming out
• when the fireworks start, start your exposure and remove the black cloth. when there's no action, cover the camera while you're still exposing, then remove when you like what you see
• stop exposure when you feel like you've got enough
-- the thing is, take a look at the "live view" when your exposure is finished writing, and adjust as needed. You've got about 20 minutes during the average fireworks display.
here's one of my better shots: