One way to help is to be sober (5)
I believe the answer is:
staid
'be sober' is the definition.
(synonyms)
'one way to help' is the wordplay.
'one way' becomes 'st' (abbreviation for street).
'to help' becomes 'aid' ('aid' can be a synonym of 'help').
'st'+'aid'='STAID'
'is to' acts as a link.
(Other definitions for staid that I've seen before include "Sedate and serious" , "Stiff; serious minded" , "composed" , "Serious or sober in character" , "Grave, sedate" .)