I have enjoyed this forum and learned a lot and I have read countless threads on pushing past the transition or "sticking point" that seems to give people trouble.
I weigh about 180 and am 5'11" and I got my rings and worked on basic pullups and dips because I was just starting to work out after a two year hiatus. After a couple weeks I could do about 8-10 pullups and 5 dips. I would work on the mu at the beginning of my workout but it was hard on my elbows and didn"t want to injure myself so I took it slow.
Here is the tip- bicycle tubes. I read about how people used them to work on their iron cross so I thought I would try it for the MU. I bought two 28 inch tubes from target and looped each one around each ring and did a pullup and put my feet in them. This gave me a slight boost on the pullup and really helped me get high enough to really work on the transition. As you move higher the assist from the rings get less as the tubes loosen so you only have slight assistance on the transistion and very little if any on the dip. This helped me get the feel of the movement and showed just how much effort was required.
This really helped and three workouts later I got my first unassisted. It was a complete max effort and wasn't pretty, but I did it. I found the mu hard on my elbows and kept doing several sets of one muscleup followed by a couple assisted trying to build up my strength. Then I had a back injury and couldn't train and at this point haven't gotten two consecutive, but after several month layoff I did a muscleup after 2 weeks of working out again.
Your results may vary, but this really helped the skill portion for me. Please realize that bike tubes are not designed for repeated stretching so flexbands or some other product will be safer, but I had no problems using bike tubes. Check everytime you get ready for signs of wear or stretching and always be aware that the could break or slip off your foot and smack you in the face. When I first started with this I put the rings low enough that I could stand with the tubes around my feet and raised the height when I felt comfortable.
Good luck, be careful, and let me know if this helps you.
Matt