Good-looking guy, notice, is following on (6)
I believe the answer is:
adonis
'good-looking guy' is the definition.
(I've seen this in another clue)
'notice is following on' is the wordplay.
'notice' becomes 'ad' (both can mean an advertisement).
'following' says to put letters next to each other.
'is' put after 'on' is 'onis'.
'ad'+'onis'='ADONIS'
(Other definitions for adonis that I've seen before include "Handsome young man (of Greek myth)" , "Aphrodite's beloved" , "Handsome fellow" , "extremely handsome chap" , "No aids (anag)" .)