Talk about class rules. Students need to know what the absence and homework policies are. If you don't allow cell phones or eating in class, it's easier to deal with it on the first day, rather than address it when it occurs. You may have to address it then, as well, but you laid the ground work on day one.
(Well... Theory is always a good way to start something. But I believe that we can't avoid the surprise of reality itself. So,I'll take this tip only as a tip!)