Partly improves personal service (7)
I believe the answer is:
vespers
'service' is the definition.
(vespers is a church service)
'partly improves personal' is the wordplay.
'partly' says the answer is hidden in the clue (part of the clue is used).
'VESPERS' can be found hidden inside 'improves personal'.
(Other definitions for vespers that I've seen before include "Evening service" , "Evening prayers" , "An hour of worship" , "Evensong - RC service" .)