Speak highly of not beginning pay increase (5)
I believe the answer is:
raise
'pay increase' is the definition.
(I've seen this in another clue)
'speak highly of not beginning' is the wordplay.
'speak highly of' becomes 'praise' (I've seen this in another clue).
'not beginning' means to remove the first letter.
'praise' with its first letter taken off is 'RAISE'.
(Other definitions for raise that I've seen before include "climb" , "better?" , "Put up" , "Breed" , "Bring up; levy" .)