Practice.

More specifically, go to the clubs you like, see what others do, try it at home.

Swaying with a beer bottle in your hand is a popular entry point.

Try to not be self-conscious - people really aren't going to care.

You won't be Turing-complete. If the DJ inserts YMCA or Macarena something else with well-known choreography, you'll have to pick up the larger pattern.