Your first instinct when dogs are fighting is to grab them by the collar and separate them, but that is an invitation to get bitten yourself! Your best approach is to grab the dogs' rear legs and lift, like using a wheel barrow (grab up by the hips, not the feet, which can cause injury). Back away from the other dog and, while still in "wheel barrow mode", turn the dogs 180 degrees so they are not facing each other. Then you can take them by the collar and lead them away. Of course this works best with two people each taking a dog. If you are alone you want to remove the more aggressive of the two dogs.
Jeff Dentler, CPDT-KA, FFCP, CTDI