Start by being honest (4)
I believe the answer is:
open
I believe this clue is a double definition.
'start' is the first definition.
(opening is a kind of starting)
'being honest' is the second definition.
('open' can be similar in meaning to 'honest')
'by' acts as a link.
(Other definitions for open that I've seen before include "Affording access" , "Frank - accessible" , "Overt" , "Undo; exposed to attack" , "Eager to receive" .)