Guide Penny away from aggressively ambitious person (5)
I believe the answer is:
usher
'guide' is the definition.
(an usher guides people)
'penny away from aggressively ambitious person' is the wordplay.
'penny' becomes 'p' (short for pence).
'away from' is a deletion indicator.
'aggressively ambitious person' becomes 'pusher' (a pushy person).
'pusher' with 'p' removed is 'USHER'.
(Other definitions for usher that I've seen before include "Introduce" , "Doorkeeper; shower to seat" , "Theatre attendant" , "Person whose job is to conduct others" , "Guide at wedding" .)