Choose to do what challenges you:

Don't have muscle up yet:
-Skin the cat 3 x 1-3
-False grip hang on rings 3 x max time (keep hollow body)
-Kip on high rings

Has 1-2 muscle ups
-Kip belly to the rings 3 x 3-5
-1 Muscle up + recovery to the kip
-1 Muscle up + try to have the second one

Has several muscle ups:
-Kip belly to the rings 3 x 3-5
-Muscle ups, recieving position on as straight arms as possibel, 3 x 1-3
-Strict MU