really the only thing you need to know to play multiplayer semi successfully is how to expand vs the AI. Once you can regularly conquer 15 provinces by the end of the first 12 turns you should be ready to go. Obviously then you will get your arse kicked by players who are better at diplomacy,scripting and strategy than you are but at least you will hopefully learn something from the experience.
Beyond that ask questions and read the guides helpful players have written and you should do ok.