I can do sets of 5-6 consecutive bar muscle-ups pretty easily without training them, just weighted chins. My advice to you is this: just get stronger. When you get stronger, everything gets easier. I recommend the following schedule:
Day 1 - Weighted chins for 3-5 x 3-5 (don't go to failure)
Day 2 - Muscle-ups
Take a day or two of rest in between and continue the rotation. The above program was designed by pullup monster John Allstadt. Doing muscle-ups every five days is not going to cut it. Pullup strength is very elusive and needs to be grooved regularly. When you can do 10 sets of 3 muscle-ups with 45 seconds of rest in between, you are in rare air.
Eventually, you should be able to do a muscle-up from the bottom. To make it easier, the movement may be initiated by rapidly arching the back prior to pulling, similar to crossfit style kipping pullups.
When you hit the wall on your heavy chin-up day, you could vary the rep schemes. Some effective rep schemes include:
5-3-2 (increase the weight on each set, with a final heavy double)
1,2,3,1,2,3,1,2,3 (the "Russian" ladder - 18 quality reps and minimal fatigue)
6 heavy singles (anything above six is overkill IMO)
Believe me, when your weighted pullups improve, your muscle-ups will get easier. Add some technique and you're set! One final tip: don't train to failure! Pullups, especially explosive variations, are a skill. Treat it as such! Keep you nervous system happy. The key is high frequency and quality reps.