A professional gets by in the correct manner (6)
I believe the answer is:
proper
'in the correct manner' is the definition.
'a professional gets by' is the wordplay.
'a professional' becomes 'pro' (abbreviation).
'gets' means one lot of letters go next to another.
'by' becomes 'per' (I've seen this in another clue).
'pro'+'per'='PROPER'
(Other definitions for proper that I've seen before include "part of Mass" , "Right, correct or appropriate" , "Befitting" , "Appropiate, right" , "Conforming to etiquette" .)