The below photo and Muscle-Up Progression explanation is from CrossFit New England, from November 12th 2011.  The photo series and explanation of the muscle-up is some of the best we've seen: 

The Muscle up Progression
The Set up: Grab the rings with a false grip with your wrists in contact with the bottom of the rings.   Set your heels up under the rings and lean back so the straps hang straight down.  Hands and elbows should be as close to each other as possible. 

The Pull:  Don’t confuse this with a pull up; the motion is different.  Instead of pulling you chin over the rings, think about leaning back (head up, chest to the sky, hands and elbows still close) and bring the handles below your chest. 

The Transition:  Time to “Whip the Pony Tail.”  Once the rings make contact with your torso the upward movement stops.  Instead think about throwing your head through to the bottom of a dip.  This is an important step – We are trying to transition to THE BOTTOM OF THE DIP, not jumping to the top of the movement.  Remember to keep the rings close to your body. 

The Dip – Just keep the rings close to your sides and push to the top of the Dip.  Yipppeee!

Sleep And Darkness  "Another thing I noticed is that it's not just the sleep but the darkness that seems important.  Even if I turn out the lights early but don't fall asleep right away, I still seem to get the benefits.  So the break from light seems as important as the actual sleep."—Matt Metzgar

The Claim: Side Stiches?  Change Your Posture  "….those who regularly slouched or hunched their backs were more likely to experience side stitches, and the poorer their posture, the more severe their stitches in exercise."—-Anahad O'Connor for the NY Times

Go Easy On Yourself, A New Wave Of Research Urges  "The research suggests that giving ourselves a break and accepting our imperfections may be the first step toward better health. People who score high on tests of self-compassion have less depression and anxiety, and tend to be happier and more optimistic. Preliminary data suggest that self-compassion can even influence how much we eat and may help some people lose weight."—-Tara Parker-Pope, NY Times