Well, mostly what you should do is described in the case posts, so I would recommend to read those carefully. For most cases, there are comments that the mods add to the posts that you're supposed to reply to when you complete a case. So if you get sorted into Team 221B, you need to reply to the 221B comment thread to get points for you and the team.
If you have questions about the language, just PM me (here or on LJ). The one thing I can think of right now is "sig tag", which is a 300x150 pixel graphic that you put below your comments when you respond to a case. It's not mandatory to have one, but you get extra points if you do it. It should be a Sherlock or Elementary graphic that has your name and team on it. You can either make one (or more) yourself, but we also have a team thread where you can request a sig tag and someone else will (hopefully) make one for you.
Oh, also there are actually three different comms that you'll get invitations for when you're accepted. One is the landomm itself (land_deduction), where all the cases and official things are posted. There's also a team comm (20021b for Team 221B) where only team members of your team have access. Some of the team challenges take place there. Last but not least there's the social comm (consultandplay) where anyone can post, and there's no restriction about what to post. Basically it's a place where all the members can talk to each other about different things.