Definately switch to Manual focus! Otherwise the annoying thing will be trying to focus while you are missing getting the fireworks.
One primary thing, USE A TRIPOD! I don't think that can be said enough. You will be taking long exposures to capture the best of it so the tripod will sturdy things.
Make sure to turn off the flash and use either Night mode or go to the shutter options and use the bulb mode if you can. You will get lots of practice seeing the streams and knowing when you want to open and close the shutter and it's better with a bulb mode. Some people use remotes and if you are at the right angle it works. All of my shots have been fairly close to under the fireworks and never that far away so I have to track through the cam and it's easier for me to just use the shutter button on the cam.
Don't be afraid to play either! I had fun last year opening the shutter and then zooming in or i would zoom in all the way to get the explosion and then zoom out for effect. Not sure how those would work at a distance but always fun to try.
Zooming:
