Write rules and pin one above blackboard (9)
I believe the answer is:
legislate
'write rules' is the definition.
I can't judge whether this defines the answer.
'pin one above blackboard' is the wordplay.
'pin' becomes 'leg' (pins is slang for legs).
'one' becomes 'i' (Roman numeral).
'above' means one lot of letters go next to another.
'blackboard' becomes 'slate' (I've seen this in another clue).
'leg'+'i'+'slate'='LEGISLATE'
'and' is the link.
Can you help me to learn more?
(Other definitions for legislate that I've seen before include "to do his job?" , "what parliament must do" , "Pass laws" , "Make rules" , "For what governments do" .)