It can vary slightly from category to category. But basically, you answer a certain number of requests (anywhere from 5 to 15, depending on the size of the category) and send the list of them (and any comments or questions you have) to support@livejournal.com. One of the supporthelps (the highest non-admin privelege level, who do most of the training, and approve screened answers on the board) in that category will send it back (usually in around a week, often sooner) with comments and stuff. You also get considered for a higher priv level. Also, some categories have formal mentoring systems. (Others, you have to ask an admin nicely and they'll hook you up with someone.)

We don't bite, really! Also, we have chat. Info's on the supportlounge profile. :)