Complicated matters should include a good plan (9)
I believe the answer is:
stratagem
'plan' is the definition.
(stratagem is a kind of plan)
'complicated matters should include a good' is the wordplay.
'complicated' indicates an anagram.
'should include' is an insertion indicator.
'a good' becomes 'ag' (I've seen this in other clues).
'matters' with letters rearranged gives 'stratem'.
'stratem' going around 'ag' is 'STRATAGEM'.
(Other definitions for stratagem that I've seen before include "Tactic to gain an advantage" , "Ploy - start game (anag)" , "Artifice" , "A cunning plan or scheme" , "Cunning plot" .)