We set out to be nice (5)
I believe the answer is:
sweet
'nice' is the definition.
(both can mean agreeable or pleasant)
'we set out' is the wordplay.
'out' is an insertion indicator.
'we' put inside 'set' is 'SWEET'.
'to be' acts as a link.
(Other definitions for sweet that I've seen before include "Amiable" , "Candy item" , "Pud" , "Afters" , "It is agreeable" .)