Gain nothing in this quarter? Be selective (6)
I believe the answer is:
winnow
'be selective' is the definition.
(winnow can mean to remove weaker options)
'gain nothing in this quarter?' is the wordplay.
'gain' becomes 'win' (synonyms).
'nothing' becomes 'O' (O resembles 0).
'in' is an insertion indicator.
'this quarter?' becomes 'nw'.
'o' placed inside 'nw' is 'now'.
'win'+'now'='WINNOW'
(Other definitions for winnow that I've seen before include "Separate the wheat from the chaff" , "Blow air through (grain) to remove chaff" , "Dehusk grain using air currents" , "Sift out" , "Fan" .)