Precede on behalf of self-esteem (6)
I believe the answer is:
forego
'precede' is the definition.
(I know that precede can be written as forego)
'on behalf of self-esteem' is the wordplay.
'on behalf of' becomes 'for' (eg speaking on behalf of or for someone else).
'self esteem' becomes 'ego' (I've seen this in another clue).
'for'+'ego'='FOREGO'
(Other definitions for forego that I've seen before include "Get ahead" , "Go without (something desirable)" , "Precede (in place/time)" , "Manage without" , "Take precedence" .)