Oktoberfest and Fruehlingsfest ('Spring festival') are a really good way to familiarize yourself with German beer!!! If you haven't been dancing on benches and tables before, this would be your chance to change this....
The beer tents are absolutely huge. There is always a band playing traditional German music, which sounds a BIT odd to start off with, but after a while you will realise that the fest wouldn't be quite the same without it. Amazingly despite the fact that most people are totally wasted, there is always a friendly atmosphere (no fighting etc. nastiness). Highly recommended!!!
Dress Code: This is not a place to wear anything fancy. As a general rule, don't take anything with you that you will miss if you loose it or it gets damaged (both of these can happen).