The rules for claiming

I know this isn't cannon (as in from the show) but what would people say are the rules for claiming? I'm dealing with it in one of my stories, and feel caught up in the mechanics. Mostly I'm trying to figure out what in a bite makes it a claiming.

So what are your opinions? I know there isn't a hard and fast rule, and I can make it work however I please in my story, I just haven't figured out what will work best in my story yet.