Summarize this article:

Stand up out of the bike seat while keeping your pedals parallel with the ground. Keep your elbows and knees loose and slightly bent, and bend at the waist so that you are positioned above the bike seat rather than behind it. When you stand up, position your head directly over the front wheel. Use the momentum you get from shifting your center of gravity back to explode straight upward. While you are pulling up with your arms, push your feet into the pedals, applying an even amount of pressure to each one.

Summary:
Ride at a slow to medium speed and lean back slightly. Sink your weight into the front wheel and then pull your handlebars upward with your arms.