Know CAO 20.7.1B.
If this is your first aircraft above 5700kg, then this will be your first practical application of it! Then work out how to use and apply it practically. If you understand it inside out and back to front to start with, it will make using it a lot easier. For example if you are doing multiple sectors without refueling, you will multiple things that are potentially limiting:
MZFW
MTOW
MLW
RTOW
RLW
Know that commuter category aircraft have a different second segment requirement (eg metro/B1900).
Also get try to prepare for multi-crew...it is a different world when you are used to doing everything yourself.