Old lover with trick said to do well (5)
I believe the answer is:
excel
'do well' is the definition.
(I've seen this before)
'old lover with trick' is the wordplay.
'old lover' becomes 'ex' (I've seen this in other clues).
'with' says to put letters next to each other.
'trick' becomes 'cel' (I can't justify this - if you can you should give a lot more credence to this answer).
'ex'+'cel'='EXCEL'
'said to' is the link.
This may not be correct. Some or all of it may be part of another bit of the clue.
(Other definitions for excel that I've seen before include "Distinguish oneself - XL" , "Be exceptionally good (at something)" , "well above average" , "Top" , "Be highly proficient" .)