Rule #1 - Be SAFE!!!
You can get badly injured and serious bitten. Dog bits are no fun, painful and take forever to heal.
If your dog is not involved - go grab him/her and take him/her away. LEASH it. Ask others to take their dogs away too. If you want to help to break up the fight, make sure, your dog is secure.
Make sure there are no kids, elderly or immobile people standing by, they might get tipped over.
Rule #2 - Stay CALM!!!
The picture below shows a dog fight situation in Asia. People who want their dogs to fight.
Most people which panic when their dogs get into an argument (re)act the same way
... they get extreme excited, loud, jelling at the dogs, adding a lot of movement and adrenalin to the situation.
You don't want to do this! There is a high chance the dogs will pick up on that energy and the fight gets more intense.
Tip #6 - Stand behind one of the dogs and grab him by his back legs. Lift his legs — much like you would a wheelbarrow — and pull him away from the other dog. As you step backward, move around in a slow circle so the dog has to side-step with his front legs. This reduces the chance of the dog turning around to bite you. Ideally, you should have another person do the same thing for the other dog in the fight.