We have no rules by the school other than start date and the ones that nat'l gives us.
We do a lot of event, like one every week or two for the whole year, not always effective, but do things that are visible, like go to a sports game, sisters all wear letters meet somewhere w/pnms and then go, you get seen in letters and their friends'll stop an say hi and sometimes sit even though they didn't plan on it. food is a good draw, ie pot luck
those are pretty good ones. look at some old threads.
good luck!