1. Form a directional order to sectional browsing. Everyone should go the same direction, aisle by aisle, to facilitate proper browsing for multiple people. Having twelve people coming from all directions doesn't help.
2. Don't push, crowd, or rush past people who are clearly waiting politely for someone else to move. Honestly.
3. Say "excuse me" if you need to get by for some reason. It's common decency. We used to have that once, when we were still British and knew how to queue.
4. Allow people to switch places with you if you are going particularly slow so that they can get to look at the stuff on the other side of you. Snails gum up the works.
5. Don't sit down in the middle of an aisle or near a shelf and start looking through the books you've already picked, especially when it's clear that other people want to browse there. Jackass.
6. Don't take other people's books. You'd think this would go without saying, but apparently people do this, and I'll have you know that I will carry a fork from this day on especially for those folks.
7. Let the folks who are trying to rapidly restock the shelves do exactly that. At a big sale like the one I went to, where things aren't alphabetical, those folks rushing in with new boxes of books are just trying to keep the stock fresh. That's good for everyone, including you, Mr. Book Fanatic.
8. Do not bring your infant child to a book sale that you know is going to be crowded and full of boxes with sharp corners. While I may be more than willing to give you leeway, others with more rabid book buying tastes have no qualms bashing your kid in the face with a box or an elbow.
9. Let old people go first. They're likely not looking for what you want anyway, and they're old.
10. Wear deodorant. Seriously.
11. Brush your teeth. Other people have to smell your breath in cramped quarters, and someone might kill you as a result...
I'm sure there are other good rules, but I'll let you all think of them. For now, that's what I've got!