Good first appearance needed for the upper crust (6)
I believe the answer is:
gentry
'the upper crust' is the definition.
(gentry is a kind of upper crust)
'good first appearance needed' is the wordplay.
'good' becomes 'g' (abbreviation).
'first appearance' becomes 'entry' (synonyms).
'needed' means one lot of letters go next to another.
'g'+'entry'='GENTRY'
'for' acts as a link.
(Other definitions for gentry that I've seen before include "who are noble" , "People of a social position just below the nobility" , "People of social rank just below nobility" , "Nobs" , "Class next below nobility" .)