Prepare round figure in part of a theatre (5,6)
I believe the answer is:
dress circle
'part of a theatre' is the definition.
('dress circle' is part of 'theatre')
'prepare round figure' is the wordplay.
'prepare' becomes 'dress' (dressing is a kind of preparing).
'round figure' becomes 'circle' (round shape).
'dress'+'circle'='DRESS-CIRCLE'
'in' is the link.
(Other definitions for dress circle that I've seen before include "best seats" , "Where to see theatre-goer" , "Part of an auditorium" , "section of theatre" , "dearer theatre seats" .)