I'll keep it short and simple:
- A tripod is required.
- ISO - lowest possible
- Focus - Use AI Servo (continuous focus on Canon) or equiavalent setting on your camera
- Aperture - small (high f-number, like f10 or above)
- Flash - off
- Shutter speed - long. Use at least 4 or 5 sec depending on your desired effect. Lower shutter speeds (4 or 5 sec) produces the "explosion ball" effect. Longer shutter speeds (15 sec) produce the "fountain" effect. If you are confident, use Bulb. Shorter shutter speeds (3 sec or less) produces just specks of light, it's not ideal but sometimes it sometimes it also gives good effects.
A few more tips:
- Remote shutter release is ideal to minimize shake.
- Other stuff on the frame aren't really bad, but ensure that your composition is good.
- Time your shots to capture the entire "explosion" from the initial spark until the light fades out (it still depends on your desired effect).
- Don't be too nervous and shoot carelessly. Firewoks displays normally last at least a few minutes. Don't be afraid that the show is too quick and will be over too quickly. Compose your shots properly. It's better to get a few great shots than several mediocre shots(I'm guilty of this).