As I mentioned previously, I like to setup my manual focus setting prior to dark. Pick a subject that is a similar distance as the fireworks will be. Since I often start my exposures with a dark sky over all focus points, autofocus does not work. Since a narrow aperture is used at a generally long distance, a wide depth of field usually covers any manual focus errors. Be careful to not bump the focus ring after the action starts. Also remember that changing focal length changes focusing in some zoom lenses. Check your lens for this attribute before dark. As a focus alternative, you can focus on the first burst that is fired.
For a shutter speed, Bulb is often best. I like to press the remote shutter release as a rocket is launching and hold it open until the firework completely fades from its explosion. This is generally 2 to 10 seconds. Missed the rockets on the first blast? You might be able to include the next set of rockets in the same exposure. Because the fireworks are constantly and rapidly moving, keeping the shutter open for long periods of time does not affect the exposure. Exposure is based on the aperture and ISO settings used. If there are subjects in addition to the fireworks included in the photo that are lit by a constant light, a specific shutter speed may be required.
You may think that a fast aperture would be helpful since you are shooting in the dark, but you are actually shooting bright light. The best aperture is usually between a narrow f/8 and an even narrower f/16. The exact setting is somewhat dependent on the distance of the fireworks (light fall-off, air clarity). Using an aperture narrower than f/16 will result in soft (not sharp) images as diffraction becomes an issue. Watch your histogram - keep the brightest pixels close to the right of the graph but not overexposed (stacked on the right side of the histogram).