Smarten up in grand accommodation (5)
I believe the answer is:
groom
'smarten up' is the definition.
(as in grooming oneself)
'grand accommodation' is the wordplay.
'grand' becomes 'G' (G is short for ground as in a thousand).
'accommodation' becomes 'room' (eg a hotel room).
'g'+'room'='GROOM'
'in' acts as a link.
(Other definitions for groom that I've seen before include "Tidy - stableman" , "Curry - husband-to-be" , "Tender of horses" , "Newly-wed; preen" , "royal attendant" .)