Notice bad habit needs guidance (6)
I believe the answer is:
advice
'guidance' is the definition.
(I've seen this before)
'notice bad habit' is the wordplay.
'notice' becomes 'ad' (both can mean an advertisement).
'bad habit' becomes 'vice' (a sin or weakness).
'ad'+'vice'='ADVICE'
'needs' is the link.
(Other definitions for advice that I've seen before include "Recommendation for a course of action" , "Suggestion for appropriate course of action" , "'Counsel, guidance (6)'" , "Formal notice" , "Opinion offered as to future action" .)