What if I told you the reason you don't have a muscle up is because your dip isn't "clean" enough?
Too often people quickly "check off" movements just because they can meet the minimum standard of range of motion. For example, "I can go down and up on rings therefore, I HAVE ring dips!" Unfortunately, not quite. Similar to other complex movements (think snatch and clean and jerk), the muscle up is built off of the pull-up and dip. If those movements aren't structurally sound, they won't provide the base needed for doing the muscle up.
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Pro tip: Practice the top and bottom positions of the dip by doing timed holds. Quality over quantity here. Complete 3-5 sets of 10-20 seconds done multiple times per week; it will go a long way. And, please use bands! Bands are a helpful way to reduce your bodyweight and ensure your positions are being held correctly. Beware: holds on the rings work your core like a mother, so you might want to take your shirt off for for this one!