Start to smoke joint and smell clean hair (7)
I believe the answer is:
shampoo
'clean hair' is the definition.
'start to smoke joint and smell' is the wordplay.
'start to' says to take the initial letters.
'joint' becomes 'ham' (ham is a joint of meat).
'and' is a charade indicator (letters next to each other).
'smell' becomes 'poo' (poo smell is a type of smell).
The first letter of 'smoke' is 's'.
's'+'ham'+'poo'='SHAMPOO'
(Other definitions for shampoo that I've seen before include "clean" , "Hair-cleansing agent" , "lather" , "My partner may be set" , "cleansing operation" .)