Way of working (5,8)
I believe the answer is:
modus operandi
'way of working' is the definition.
(someone's usual way of working)
This is all the clue.
(Other definitions for modus operandi that I've seen before include "this shows how it's done" , "Particular way of doing something (Latin)" , "Method of working" , "way of doing things" , "MO in full" .)