The first thing to remember is that you are photographing a burst of light. This means that the aperture (f-stop) is what will control the look of the fireworks when you photograph them. If they are too bright use a smaller aperture (larger f-stop) so that the colors don’t get burned out. If they are not bright enough use a larger aperture to let in more of the light from the durst. With the instant feedback you get from digital cameras you can see if you are using an aperture that is allowing enough light in to make a good exposure.Your shutter speed can be as short one second or as long as you like if you are just getting the blackness of the sky. Do you want one burst or several in each frame? This will help you choose your shutter speed. Shorter shutter speeds will allow one or two bursts and longer shutter speeds will allow many more. Most displays are set off via timer and you can see the sparks from the mortars as they fly into the sky. Count and get the rhythm so you can gustimate how many bursts you will get in your image. Just remember, all bets are off when they start the finally! In the finally many mortars are fired in very close succession. Shorter shutter speeds are in order here to avoid serious overexposure.
Is there a cityscape or other scene that you want to have in the image? The best way to get both a cityscape and the fireworks in the same image is to use a shutter speed that will give you a well exposed cityscape. Start zeroing in on your exposure for that by starting a little before the fireworks start. Remember to check your exposure once the display starts because the flashes of light from the fireworks will add light to the scene.
In either of the above cases you will want to start with an aperture of f11 or f16 and go from there.Another thing that will make the night a lot more successful is to shut off autofocus. In fact you can make sure that your images are tack sharp by using a trick that I use for Night and Low light photography. Focus your lens at infinity and then tape in down so it cannot be moved. This works well with any lens because you will be far enough away from the fireworks that your lens will need to be focused at infinity anyway. If your lenses don’t have a window so you can see where infinity is, here is a trick you can use. Go out earlier in the day, using auto focus, let the camera focus on a distant object. Now with a bit of art tape or painter’s tape, tape off the focus ring on your lens.Be sure you don’t tape down the zoom ring on your zoom lenses! Do this to all the lenses that you think you will use and you are good to go. You can change lenses and not have to worry about refocusing. REMEMBER to turn off the autofocus for the night! Having the camera try to focus while the focus ring is taped down can ruin the nylon gears in your camera or lens.
As many of the posts about photographing fireworks say, use a cable or remote release if you have one. If you don’t all is not lost because your camera has a self timer. Set the self timer to its shortest time. Some can be set for as little as two seconds others have a standard ten second setting. Either way this will help you get nice sharp images with no camera shake. Another thing to do is turn off any vibration reduction when your camera is on a tripod. Using vibration reduction when the camera is mounted to a tripod will reduce the sharpness of your images. This has to do with the way vibration reduction works.
I hope this helps you get some great fireworks images!