Comedian’s act is run-of-the-mill (7)
I believe the answer is:
routine
I believe this clue is a double definition.
'comedian's act' is the first definition.
(I've seen this before)
'run-of-the-mill' is the second definition.
(thesaurus)
'is' acts as a link.
(Other definitions for routine that I've seen before include "Method" , "Variety act" , "Regular procedure" , "Unvarying set of actions" , "Nine to five?" .)