Heavily used when preparing to play the pantomime villain, eastern boy Prince Lew, maybe? (7,6)
I believe the answer is:
eyebrow pencil
'heavily used when preparing to play the pantomime villain' is the definition.
(pantomime villains often have thick eyebrows)
'eastern boy prince lew maybe?' is the wordplay.
'eastern' becomes 'e'.
'maybe?' indicates an anagram (I've seen 'maybe' mean this).
'boy'+'prince'+'lew'='boyprincelew'
'boyprincelew' is an anagram of 'yebrowpencil'.
'e'+'yebrowpencil'='EYEBROW PENCIL'
(Other definitions for eyebrow pencil that I've seen before include "Cosmetic item" , "Cosmetic applicator" , "Cosmetic in stick form" .)