If There's One German Phrase You Memorize, Make It This One
31/32"Prost!" is "cheers!" in German, so you will definitely want to practice using that phrase before you go. Essentially, if you run into a language barrier mid-conversation during the festival, just saying "prost!" and offering to clink beers will smooth it all over.
You should also know that the liter steins of beer served at Oktoberfest are called "masses", so knowing "ein mass, bitte" (one mass, please) will also get you far.