Heartbreaker Tom assumes right to be good looking (6)
I believe the answer is:
pretty
'be good looking' is the definition.
'heartbreaker tom assumes right' is the wordplay.
'heartbreaker tom' becomes 'petty' (frontman of Tom Petty and the Heartbreakers).
'assumes' is an insertion indicator.
'right' becomes 'r' (common abbreviation).
'petty' placed around 'r' is 'PRETTY'.
'to' is the link.
(Other definitions for pretty that I've seen before include "Fair - fairly" , "See 19" , "Attractive - quite" , "Fairly; appealing" , "Pleasing on the eye" .)