Before the display starts: pick the fastest aperture you can, focus the camera on something lit and distant (>50m or so, depends on your camera's depth of field and the display distance but that's probably far enough). Once you've set a distant focus point, turn off autofocus so it stays on that distance - it may struggle during the display to lock.
Keep the lens wide so camera shake has less effect - you'll want it wide to capture the larger breaks anyway.
If you want light trails, this is all about keeping your body stable so you can shoot with a slow shutter. Try to be still as you press the shutter, you can use a small shutter delay or motor drive to help. How slow depends on how good your camera's image stabilisation is, and how still you can hold your body while pressing the shutter. I can go down to 0.5" - 1" on my Olympus and still get a reasonably number of sharp shots, but they all differ. I usually start faster (around 1/10th and iso400) and slow the shutter down till I find where it starts to go too blurry, bumping up the ISO if needed.
If you don't want light trails, just push the ISO up as far as you dare. Remember to review a few times and zoom in on the review to see how sharp/wavy your light trails are.
I usually shoot fireworks in shutter priority or full manual, if you're using auto-exposure dial down the eV to -1 or -2 so the camera doesn't try to make a night sky look 18% grey!
Are you somewhere where the clouds/sky will reflect a lot of orange street lights? I usually shoot fireworks with daylight white balance so the colours don't wash out - but you can get orange clouds/sky from street lights.
Good luck and remember to enjoy it!