Trying to reform smoker, I must take the lead (7)
I believe the answer is:
irksome
'trying' is the definition.
(I've seen this in another clue)
'reform smoker i must take the lead' is the wordplay.
'reform' indicates anagramming the letters (letters in a new form).
'must take the lead' means one lot of letters go next to another (some letters go at the front).
'smoker' with letters rearranged gives 'rksome'.
'rksome' after 'i' is 'IRKSOME'.
'to' acts as a link.
(Other definitions for irksome that I've seen before include "bugging" , "'Tedious, tiresome (7)'" , "Tiresome, irritating" , "Burdensome and tedious" , "Smoker I find annoying" .)