Try going through the proposed welcome message by theymos, it is yet to be implemented, but it contains a broad overview of the forums guidelines and regulations compiling that into a succinct, easy to read text.
*Follow the link to get the full post
Here's a draft of a welcome message for new users. The user will see it on the screen confirming their registration, and it'll also be available in the help center at any time.
There are also detailed explanation on the various boards and sticky threads to help you out, if you're willing to read them.