Step 1: Throw a Breakaway

Picture of Throw a Breakaway
The first step is to throw a breakaway. It doesn't really matter if you mount a trapeze or just go to a sleeper, but it is important that you throw a breakaway instead of a frontstyle power throw, because the spin of the yo-yo helps "suck" in the string into the gap instead of pushing it out.

I'd probably recommend learning it from a sleeper, 'cause it gives you more time to whip the string around... and more time means you can shout "SONIC BOOM" and get the dramatic motion in, too.