How do I trim lavender?

Somebody recently asked me how to trim lavender.  You can prune it back every year to keep it the size and shape you want.  Or you can let it grow bigger by never trimming it.  The important thing is this:
 - prune lavender in the Spring
 - don't prune out more than about half of the plant (I've killed lavender pruning it too much in one go)
 - don't prune lavender in the Fall.  Like most Mediterranean perennials, it resents Fall pruning.
 - after lavender is finished flowering (usually by the end of June here in Utah) shear off all of the flower stems and it will bloom again.