Good puff with exercise embracing sweetheart (5)
I believe the answer is:
adept
'good' is the definition.
(synonyms)
'puff with exercise embracing sweetheart' is the wordplay.
'puff' becomes 'ad' (short for advert - a puff piece is an advertisemen).
'with' is a charade indicator (letters next to each other).
'exercise' becomes 'PT' (Physical Training).
'embracing' means one lot of letters goes inside another.
'sweetheart' becomes 'e' (the heart/centre of 'sweet').
'ad'+'pt'='adpt'
'adpt' placed around 'e' is 'ADEPT'.
(Other definitions for adept that I've seen before include "One who is very skilful" , "One highly skilled could be taped" , "Having the required skills" , "One very skilled at work" , "Master" .)