Watch a video of a punk rock concert and study how the audience moves. Observing others is a great way to learn new skills before you try your own routine.
Put on your favorite punk rock CD and raise one fist in the air. Thrash your head from back to front and plant your feet. This is your rock pose, come back to this at the beginning of each song and during rocking guitar solos.
Kick your legs out in front of you; punch the air when the music picks up speed. Keep banging your head and feel free to yell obscenities or simple battle cries. Other dancers may bump into you -- a common occurrence in mosh pits -- so be ready to push them away.
Add in dance moves that you studied and let your body take over. Keep moving and you won't be considered a stiff.