Basic Photography

Ask any photographer what they want to take pictures of during the Fourth of July and you will probably get the same answer. While everyone loves the food, festivals, and general craziness that goes on around Fourth of July celebrations; it is what happens after the sun sets that really gets photographers excited and nervous. Fireworks photography is notorious for missed shots, shaky images, bad exposures, and out of frame subjects. However, fireworks photography really is not as hard as you have been led to believe.

FramingFireworks do not explode in the exact same spot every time. Because of this plan on taking a wider shot than you would normally do. You will need to crop the image or have your lab crop the image for you to correct framing.
FocusFireworks move fast and your camera's autofocus may have trouble with them. It is best to either prefocus or set your camera to manual.

ExposureFireworks are very bright but the amount of light created during a fireworks show varies greatly. The first few explosions are generally far enough apart that a relatively long exposure time is possible. The space between explosions will also allow you to capture the shell flying into the air, the explosion, and the full extent of the explosive display. When the display reaches its finale there will be much more light and the shells will explode rapidly. In order to make an image from this situation you will have to increase your film speed in order to decrease the exposure time.

Leave your aperture on a high setting so that the entire explosion will be in focus.

Source http://photography.about.com/od/takingpictures/qt/Fireworks.htm