As John mentioned, smoke is the bane of the fireworks photographer. If you can, find out where the fireworks are actually being launched from and position yourself such that the prevailing winds will carry the smoke on the far side of the blooms.
Fireworks themselves are simple to shoot: Set your camera up on a tripod with a remote release (These two things are essential), and select a focal length which will ensure that you capture all of the blooms, and with any luck a little of the surrounding city-scape. The best fireworks shots generally have something in them besides just the fireworks.
Set your camera/lens to manual focus and focus on infinity. Set your camera to manual exposure, and select a medium to low ISO (<400). Use an aperture of f8, and start with a shutterspeed of 2 seconds. Watch the launch point (I bring binoculars for this purpose) and you usually tell when the firework has been launch by the trail of sparks going up from the launch point. Trip your shutter, and wait.
Once it's completed the exposure, review the image and decide if the trails are long enough and adjust your shutter-speed accordinly if desired. A shorter speed will result in smaller, more 'frozen' blooms and a longer speed, longer, more flowing blooms.