Things I would review that tend to be weak areas-
Oral:
-Be able to list the factors affecting VMC as well as how the aircraft is certified
-Multi engine systems (not just semi systems)
-Make sure you get as much info as you can from the stage pilot before attempting to answer a takeoff scenario based question (i.e All performance info, runway info, airport info, wind strength and direction, ect)
-Commercial ops regs
-Review all basic info from previous stage because its all fair game
Flight:
-Overall Instrument procedures are usually a weak area. Make sure you know your profiles and understand what checklist is appropriate in what situation.
-Take a proficiency flight before the stage if you can. You would be surprised how quickly your skills will diminish.