Ready to get a chair (4)
I believe the answer is:
seat
'chair' is the definition.
(something to sit on)
'ready to get a' is the wordplay.
'ready' becomes 'set' (set can mean ready or prepared).
'to get' is an insertion indicator.
'set' placed around 'a' is 'SEAT'.
(Other definitions for seat that I've seen before include "MP's constituency" , "Position (in parliament)" , "Box ---, position of advantage" , "Behind" , "See 10" .)