Run round hillock, holding horse back (8)
I believe the answer is:
organise
'run' is the definition.
(run can mean to organise or control something)
'round hillock holding horse back' is the wordplay.
'round' becomes 'o' (round can mean a round object).
'hillock' becomes 'rise' (I've seen this in another clue).
'holding' means one lot of letters goes inside another.
'horse back' becomes 'gan' (I can't explain this - if you can you should give a lot more credence to this answer).
'rise' going around 'gan' is 'rganise'.
'o'+'rganise'='ORGANISE'
Can you help me to learn more?
(Other definitions for organise that I've seen before include "run" , "Devise and direct" , "Arrange in a systematic or orderly way" , "Arrange, plan or direct" , "Set up, co-ordinate" .)