DZgirl- you go to MTSU, don't you?!? That's where I am. My roomie last Spring was a DZ at MTSU also!
Well we have a pretty successful points system where each event is worth a certain # (i.e. rituals worth more pts than meeting, meeting more pts than intermurals/mixers, etc). We also occasionally give prizes to people with the most points at the end of the month/semester/yr.
We rarely have problems getting newer members to stay active, but the Seniors get really busy so the officers have to sometimes keep on their tails about it.
If people don't enough points by a certain time, or owe any money to the chapter, our officers don't allow them to go to "fun" functions until they get back into gear. This works well b/c most of the people who we never see at meetings and service projects will show up out of nowhere for mixers and crush parties, and they're basically told "Sorry, but you should have attended the mandatory events."