Sticky to answer your question I will take you to the past year's GRumble. And I'm glad that you asked actually. All new members should join and become a part of the tradition.
GRumble Sign-Up...what this thread is.
GRumble Publicity...a failed attempt at entrant involvement
GRumble 2011
GRumble 2010...my first year running GRumble
GRumble 2009...used's last year running GRumble
Basically Singles is about pitting yourself against another awesome member and finding out who your peers think is better. Better has a very vague meaning in this case.
For Doubles, you need to find yourself a teammate, make up a name and construct matching jerseys. You then pit yourselves against other teams. Huzzah!
It's more or less a "popularity" contest. But there's always an upset or two along the way. It's fun and it gets us talking and visiting the forums. Some people float by on their reputation, but I can easily say that increasing your visibility on the site usually increases votes for you. Make some threads, comment on other people's stuff, kiss ass.
Please guys leave suggestions if you have any. I'm thinking that there will probably not be a GRind or a Publicity thread this year. Registration will probably end when the excitement of signing up has.
Let's make this a big year. If you have people on friends list on PSN, XBL or Facebook, invite them to participate.