Begin painting a good man first (5)
I believe the answer is:
start
'begin' is the definition.
(I know that begin can be written as start)
'painting a good man first' is the wordplay.
'painting' becomes 'art' (painting is an art).
'a good man' becomes 'st' (abbreviation for saint).
'first' means one lot of letters go next to another.
'art' after 'st' is 'START'.
(Other definitions for start that I've seen before include "Onset" , "Commence" , "Move quickly < when surprised" , "Begin - jump" , "Begin to recoil?" .)