Prepare most of cereal order (5)
I believe the answer is:
doric
'order' is the definition.
(Doric order is a classical architectural order)
'prepare most of cereal' is the wordplay.
'prepare' becomes 'do' (I've seen this in other clues).
'most of' means to remove the last letter.
'cereal' becomes 'rice' (rice is a kind of cereal).
'rice' with its last letter taken away is 'ric'.
'do'+'ric'='DORIC'
(Other definitions for doric that I've seen before include "In a classical Greek style of architecture" , "A classical style of architecture with fluted columns" , "Denoting a classic Greek style" , "One classical order in architecture" , "hairdo tips costly, for the most part" .)