Don't worry if you can't remember the exact sequence anymore - lots of people don't. The important thing is that you don't get all tense about it, just go with the rhythm of the group.
The basic idea: you slap your thighs alternately with both hands, then you clap your own hands, then you do a movement (some people raise their arms, some point at their neighbors or themselves), and the whole group shouts "Schnitzelbank!" in sync. The tempo is pretty fast and often gets faster. Each round follows the same pattern, but the movements in the middle (between the claps) can vary - sometimes it's hand movements, sometimes funny gestures or even little jumps.
Honestly, the thing is so different from region to region that there's no one right version. When you get there, just watch how the others do it and join in. If necessary, ask your friend beforehand which version they play. Most people are pretty relaxed about it and happy to help if you don't nail the rhythm right away. The main thing is that you have fun doing it.