Staff more optimistic following Conservative leader (7)
I believe the answer is:
crosier
'staff' is the definition.
(crosier is a kind of staff)
'more optimistic following conservative leader' is the wordplay.
'more optimistic' becomes 'rosier' ('rosy' can be similar in meaning to 'optimistic').
'following' says to put letters next to each other.
'leader' suggests taking the first letters.
The first letter of 'conservative' is 'c'.
'rosier' put after 'c' is 'CROSIER'.
(Other definitions for crosier that I've seen before include "Ecclesiastical staff" , "A bishop's staff as symbol of office" , "Bishop's crook" , "Staff carried by a bishop" , "one's hooked!" .)