Do well, being expert and well-trained (6)
I believe the answer is:
profit
'do well' is the definition.
(I've seen this in another clue)
'expert and well-trained' is the wordplay.
'expert' becomes 'pro' (short for professional).
'and' is a charade indicator (letters next to each other).
'well-trained' becomes 'fit' (I've seen this in another clue).
'pro'+'fit'='PROFIT'
'being' is the link.
(Other definitions for profit that I've seen before include "Clean up" , "Financial gain" , "returns" , "Gain, return on investment" , "Surplus earnings" .)