Some good tips there.

Definitely make sure the flash is completely off or, as that picture shows, it will shorten the depth of field and you won't get the fireworks as the main focus of the image.

And a long exposure time is definitely needed, which works best with a tripod so you don't end up with some camera shake spoiling the image. A free alternative is to find a fence or wall then you can rest your elbows on when you take the shots to steady yourself.

And use a manual focus as any autofocus won't work at night while pointing at the sky. Just set the focus to infinity or the furthest it will go.