There are a few rules, but applying some basic common sense should be enough to ensure you have an enjoyable time. While there are plenty of tourists each year the majority of the festival's guests are Bavarians. If you really want to join in, you can dress up in Lederhosen or Dirndl. There are several hire shops in town. Just be careful not to become one of the Bierleichen, or 'beer corpses', sleeping off one Masstoo many in the gardens.
It's not all beer and bratwurst; there are lot of fairground rides, candy floss stalls, shooting galleries, and a puppet theatre. You can find cakes and strudels, and even some wine. Still, if you don't like beer or meat this might not be the best place for you. Most tents offer traditional Bavarian music (oompah to the max), although only some have live bands, and if you want to accompany that with some Bavarian folk dancing then make for the Herzkasperl tent.
This year the festival runs from 22 September to 6 October. You can find out more on the official Oktoberfest website. There's also an official app that will help you navigate the festival, and the rest of Munich too.