"Fortunately, Rockstar must have realized that they left something out in their instruction manual because they've recently published a PDF dedicated just to multiplayer gaming.
The guide is filled with interesting tips and info. For instance, they explain how Party Mode work, something that has been driving me crazy since the launch. Turns out that when playing team modes, the game tries to find a similarly sized party to match you up with. In competitive modes it just fills up the slots with people and gets you going.
There are also plenty of usefull tips in the guide, like using blip settings to tweak your difficulty setting, and how auto-aim is an "awesome feature" that is often misunderstood and absolutely doesn't level the playing field."
Hit the jump for the full guide.