The best thing is to just get involved in a good one and stick with it. We have one here in Australia, the Fishbowl, that has 36 teams, is in its 4th season. We have a write up of every single game, there are weekly MVP points, we have all the managers organised into 4 big Federations. There are prizes of free supporter at the end of the season for the coach of one of the MVPs and one of the managers on the winning federation. We have 4 private federations with hundreds of posts as well as our public league forum which has dozens of threads but the main thread just past 6,000 posts.
Once you have found something like that you will never need to look again.