I'll second the location thing as being my #1. I like one of the trashcans on Main St just past Casey's. I ended up using the one near the info board.
I set my tripod on top of the trash can rather than open it all the way on the road or sidewalk. Worked out great.
For settings: they can vary slightly, but generally Manual priority. ISO 200, Aperture: f/8-f11 and shutter speed anywhere from 2 seconds to 6 seconds. I mostly used a 5 second shutter for mine. Focus on the castle. Once its in focus, switch the camera and lens to manual focus, this way the camera wont try and refocus each time you release the shutter. You don't have to, but it might help.
If your comfortable and want to get a bit creative bring along a small piece of black cardboard type paper with you. Just big enough to completely cover the front of your lens. In manual priority set the shutter to "BULB" (ISO and f/stop you can use from above). As the fireworks start, release the shutter. When the first wave or bursts stop, cover the front of the lens with the black paper, getting it as close to the lens as you can without touching the lens. Then when the next wave of fireworks bursts start remove the paper from the lens. Do it once or twice like this then close the shutter. I wouldn't do it for more than 20 seconds or so. This will combine a few different bursts together in one shot. You can create a similar image during post processing, but sometimes its fun to experiment while your actually taking the picture.
Also during the finale, since there are so many bursts going off at the same time, getting a good picture is very hard because of over-exposure. Try shortening the shutter to 2 seconds and closing the aperture to f/16-f/22 to help isolate the streaks.
If you don't do either of the last 2 suggestions, no big deal. Just thought I put some possible options out there.
Have fun!!!