1. Read the FAQ! We have too many newcomers (and actually, I did this too) that post a question in HelpDesk that also happens to be on the FAQ. We really need to make that thing more visible...
2. Read the rules, too. Just click the "rules" button on the header toolbar.
3. Other than that, all I have to say is, well, have fun. I'm sure everyone's a bit nervous upon joining (surely I wasn't the only one...), but we're a good community and you don't have to worry about anything. Just be nice and enjoy it here!