This is how I did it.
First figure out what team you want to do. Teen Titans? Justice League? Legion of Doom? Then decide how many people you want on the team. You can ask others if youj want, but this one is your call. Personally, I went with 12 man teams.
Next you have to research. Make a list of everyone that's been on that team. Include spin-off teams, honorary members, notable alternate reality versions, etc. Prepare yourself some kind of document so you can keep track. When I did this, I used a spreadsheet and I spent several days checking different wikis.
That's to get you set up.
Once you start, list ... 25 to 50 characters.
Each charter starts with ten point. No character can get below 0. No character can get above 20.
Once every five posts or three characters, whichever comes first, the posters taking part in the game get three points.
They can add three points to a character. They can take away three points from a character. They can add one point to three different characters. They can take away two pointys from one character and add one point to another character. However they want to split their points.
You, as the person running the game have to check the posts at least every day or two. Every character that has zero points, you need to remove from the posts and replace with another character from your document, starting them out with a fresh ten points.
The game is over when your document has no more characters, and the number of characters left on the post matches whatever number of characters you wanted to have on your roster.
Then, to close everything out, make a picture for your team.
Here's the roster we made for the JLA last time we played.
(Sadly, I don't think I have any off the other team pictures.)