In my experience, I have found that you actually really need 10+ owners to make a league fun. With just 4 owners, every team will be completely stacked, and winning and losing is just random. But if you're adamant about just 4 owners, so be it. Just something I've observed that the leagues I've played in have been less fun with fewer members.
As for tips, I can't really say too much. I find fantasy leagues to be inherently fun just the way they are. Not much needs to be spruced up with the concept. I would suggest doing a live draft (if it is feasible). It is loads of fun to talk trash, drink beer (if you're of age of course), and pick your team yourself. The draft itself is perhaps my favorite part of fantasy sports, so I try to go all out and make that an extravaganza.