Help idiot start to improve posture (10)
I believe the answer is:
assistance
'help' is the definition.
('assistance' can be a synonym of 'help')
'idiot start to improve posture' is the wordplay.
'idiot' becomes 'ass' (I've seen this before).
'start to' suggests taking the first letters.
'posture' becomes 'stance' (stance is a kind of posture**).
The initial letter of 'improve' is 'i'.
'ass'+'i'+'stance'='ASSISTANCE'
(Other definitions for assistance that I've seen before include "Aid" , "Help" , "Support" .)