Make sure they're already walked and home before the fireworks start, and that they've been out to relieve themselves.
Keep them indoors. Keep the curtains shut, keep the lights on, turn up the volume on the telly, settle in with them and relax, emit an "everything's perfectly normal and not worth getting worked up over" kind of attitude. Don't overfuss the dog if and when he reacts to the fireworks. Let him go to a place he feels safe, if that's what he wants to do, but don't follow him cooing and fussing, leave him be. Show him there's nothing to worry about by acting like there's nothing to worry about. Set a good example by staying calm yourself.
You can give them a nice bone or a kong, something they'll enjoy concentrating on to distract them. Or a favourite toy.
There are calming herbal supplements that might help too. Or even meds from the vet if the dog is liable to get very distressed.
It depends on the individual dog as to what will work best to keep them comfortable, but this is generally the way to help anxious dogs during fireworks.