When joining to the simulation, introduce yourself as people may not be able to relate your 4-character SimSig ID to your forum ID or name. This is best done through the SimSig messaging as everybody sees it. However, other communication can take place by whatever means appropriate - VoIP, Messenger, or whatever. If you're a newbie, don't be afraid to say so as people will be willing to help you.
Newbies and experienced users often join a session simply to observe and learn. This is particularly useful when a new simulation appears as it gives you a chance to see how the simulation works, its pecularities and what rules apply where.
Let the host know if you are only observing or alternatively wish to take an active role.