As others have said -
Know regs and ops manual
know ur aircraft
contact foi who is conducting it sometimes they give you a study guide sheet with references to know...
Think practical as well as they will through scenarios at you and expect a practical application and understanding of your role...
Just remember your not their alone - contact the cp your replacing as some fois and different ops will have their own intricacies.
Overall study hard, be confident and relax. The last thing you want to be is a blabbering idiot.
My first one was very straight forward. The second cp job I had was after the previous candidates failed numerous times making mr Casa overly cautious and ridiculousy thorough. In the written be sure to write references and break down 3 sections to your answer - the reg the answer and how it affects u. The oral just think before opening your mouth... Be confident, and if your unsure indicate how you would overcome this I.e call foi or reference etc. For the flight just take your time and ensure you do everything by the book... This includes all checks briefs checklists etc. I.e use your checklists and operate to your ops manual exactly not just there or thereabouts. Check weather and notams carefully as with mels.
About all I can think of... Oh understand legal perspectives of your role... Check things like due diligance and negligence. management methods, Risk assessment, threat and error management, safety systems etc.
Check 82 48 and know them to death...
Any queries pm me if you like it wasn't long ago I did a recent assessment...
Cheers
Rob