Decorating site for play — this tells theatre folk what to do (5,9)
I believe the answer is:
stage direction
'this tells theatre folk what to do' is the definition.
'decorating site for play' is the wordplay.
'for play' indicates an anagram (I've seen this in other clues).
'decorating'+'site'='decoratingsite'
'decoratingsite' with letters rearranged gives 'STAGE DIRECTION'.
(Other definitions for stage direction that I've seen before include "order" , "exit as one" , "actor will carry it out" , "exit, say?" , "exit, maybe" .)