Dancing actress covers excellent steps (9)
I believe the answer is:
'steps' is the definition.
(I've seen this before)
'dancing actress covers excellent' is the wordplay.
'dancing' is an anagram indicator.
'covers' is an insertion indicator.
'excellent' becomes 'ai' (resembles 'A1', old-fashioned term for excellent).
'actress' is an anagram of 'strcase'.
'strcase' enclosing 'ai' is 'STAIRCASE'.
(Other definitions for staircase that I've seen before include "Way between floors" , "Indoor flight" , "Route between floors" , "Group of joined locks on a canal" , "A group of linked canal locks" .)