RFC 1855: Netiquette Guidelines
RFCs (Requests for Comments) are the working standards of the Internet; while a very few are eventually promoted to official Internet Standards, most never do, and yet are no less important for that. Some are superseded; some obsoleted; but most are still in effect.
RFC 1855: Netiquette Guidelines (dating back to 1995) is one such RFC. It’s an important document, and should be read by all newbies.
Its guidelines are not mandatory in letter but rather in spirit (e.g. I use underscores rather than asterisks to indicate emphasis in plain text). Much as a great poet knows when to break the rules, so too an experienced user knows when the time is right to do things differently. A newbie, though, should always follow the established pattern until he has the experience to know when not to.