1. Know your internal process and operation inside and out
2. Know what problems and processes are to be improved after implementation
3. Keep a log of users requests. If you're the project manager, make sure every request the users has comes to you first before sending to the consultant.
4. Read through the proposal from the consultant to know what they're delivering and what modifications they'll make
5. Make sure you have everyone in the company on board with the change.
These are just some that came to the top of my head. I'm sure there are more.