First off, let me say Happy Birthday to my sister! Quite appropriate that I'm talking about sibling rivalry during her birthday week. I have to say, we didn't fight all that much growing up, though when she was a little older, about 10, and I was only 7, I wasn't included as much when her friends popped over. And the middle school years were a bit rough -- but they were rough for everyone, right?
Siblings do fight. Some more than others, some in different ways, some more physical, others more of the yelling variety. Fighting. No mom wants to hear it. But what do you do when they lay into each other? Stop it before the blood starts to flow, sure, but there are some other really good ideas out there, ones that when I read them, I thought, "Oh, wow...that makes total sense!"
-- Don't judge or place blame. Instead of asking "What did you do?" to either kiddo, even though you may very well know, that sets up and enforces "roles" for the kids, which can be hard to shake as they grow. Try to have everyone take deep breathes and get them calm first. Then ask them to "Tell me what happened. Help me understand." If you have a younger child that may not be able to really communicate, help him or her with words.
-- If you can avoid it, don't get involved. They will get used to you being referee and helping. If they are figuring out a toy situation or territory issues, let them do it themselves (though, obviously, if someone is going to get hurt, so what you have to do). If there is teasing or name-calling or other behaviors that go against your house rules, point that out and enforce that, but don't "rescue" a child or "fix" the specific situation. Have them handle it.
-- If you have to mediate, instead of telling them what to do, ask questions. Ask them to think of ways to get out of the situation (What do you two think is a good solution to this? What do you think is fair?).
-- Punishments don't work. Taking away toys, sending both kids to their rooms, and the like will only model that punishing works...and then, next time, the kids will "punish" each other. If you can, solve the situation with a respectful outcome, a win-win outcome, which will encourage them to choose that next time.
-- Praise them when they don't fight. When they have cooperated and figured out a way to play together despite a stumble or two, praise them together and individually.
Do your kids fight? What do they fight over and what works in your home to ease the tension?