Rule two is: Respect the DM. They are in charge, and if you don't like it, leave.
Following those two rules is all you really need to know. Do some research on whatever game you're looking to join a group on (get your bearings--people help noobs who help themselves), and be brave! I'm certain people will be overjoyed to have a new member who follows the Rules ^ and brings enthusiasm and creativity.
This is what I've learned from my (very young) days playing D&D.