I wouldn't try making any rules. They'll just ignore.
Do you read near the end of the lesson? They tend to be more relaxed then after 40-45 minutes of games and tend to sit down and pay attention.
Sit a bit higher than them, and make sure that everyone can see the book. With the odd trouble makers, I usually put my arms on my hips and make the "teacher-is-not-very-happy" look. Worse comes to worse (and with the parent's permission) I sit my daily uncontrollable student/s on my lap and try best to read the book.
Do what you can. I think I've only had 3-4 successful reading lessons, the kids are just too hyper to stay still for too long.