Short dress wearing good looking girl will detract (8)
I believe the answer is:
'detract' is the definition.
'short dress wearing good looking girl will' is the wordplay.
'short dress' becomes 'mini' (I have seen 'Short dress' mean 'mini' so perhaps 'dress' could also mean 'mini'; 'short' suggests an abbreviation).
'wearing' is an insertion indicator.
'good looking girl will' becomes 'dish' (I can't justify this - if you can you should believe this answer much more).
'mini' put into 'dish' is 'DIMINISH'.
Can you help me to learn more?
(Other definitions for diminish that I've seen before include "Make smaller or less" , "make shorter" , "Contract" , "Diet" , "Make less with mini dish" .)