This is a shot I took a few year ago when teaching myself how to shoot fireworks. The trick I found to fireworks is to use a tripod and a long exposure. In this one I used an f/22 to help with both the long exposure and to also help keep as much in focus as possible. I set the shutter to bulb so I can control when it opens and closes. I positioned my camera to about where the fireworks were exploding and and opened the shutter. After I let the shutter stay open for abut 30 seconds. Any longer and my photo would start to capture too much light. Another trick you can do is open the shutter and place a piece of black paper in front of the lens and remove the paper when ever the fireworks go off and then recover and wait for the next one. This would let you get multiple fireworks in the photo without over exposing the background.
ISO: 100 | Aperture: F/22| Shutter: 33sec. | FL: 18mm