Regent's man ordered to follow a king's plans (12)
I believe the answer is:
arrangements
'plans' is the definition.
(I've seen this before)
'regent's man ordered to follow a king's' is the wordplay.
'ordered' is an anagram indicator.
'to follow' means one lot of letters go next to another.
'a king' becomes 'ar' (I've seen this in other clues).
'regents'+'man'='regentsman'
'regentsman' is an anagram of 'rangements'.
'rangements' after 'ar' is 'ARRANGEMENTS'.
(Other definitions for arrangements that I've seen before include "orders" , "Plans for a future event" , "Organisation, disposition" .)