This skill takes a while but is _so_ exciting the first time! Practise on a wooden gym floor or similar. If you practice outside you will eat up tires like never before. If this becomes a problem, look for a harder rubber tire. Generally these are the ones that mark up floors, so don't use one if you ride in & out.
Once you feel confident try starting the spin with your arms out and tucking them in sharply just as you hit the pirouette. You'll get about 4 revolutions in under a second (and a big round of applause from passers-by). Be careful when going this fast, though. If you actually do 4 revolutions in under a second, the subsequent fall will probably be HARD! Rather than spin super fast, of course, it looks better to be able to ride out of it.
You could also work up to the ballerina style where you try to look in one direction for as long as possible and then whip your head around. This is pretty difficult, though.
Further variations include riding out backwards; do this smoothly, and increase the size of the circle while going backwards and it looks _awesome_.