Moms Talk Q&A: Dealing with Sibling Rivalry

I have two younger sisters and we had our fair share of fight as children and teenagers—over everything. They were the pretty typical fights, over stuff like whose turn it was to sit in the front seat and over who borrowed who's shirt and Moooom, she's making that face at me again! 

As adults, our relationship is great, but it was some hard years there for my parents. 

How do you mediate fights between your kids—or do you? Do you let them fight it out or do you step in? What's the best way to promote healthly relationships between siblings?