What are some good ideas on filming a doentary?

My friend and I are planning on making this graduation gift, by filming our clmates through the whole year and the problems and situations they go through. So, we are sort of doing a Laguna Beach/The Hills-esque movie. But our problem is, we have 50 or more students in our cl, and we cannot just focus it on a single student. How can we be able to make a Laguna Beach-esque movie, when we are not using any scripts and everything is just candid? Or do you have some other ideas on a better doentary without focusing on just one person?