Hi there-
The exact details of your preoperative visit are going to vary quite a bit between practices, and will also depend on your medical history and the details of the procedure you are having done...
In most cases, this visit serves the purposes of confirming your goals, assuring you and your surgeon are "on the same page", obtaining your informed consent to the procedure planned, having any remaining questions answered, giving you your prescriptions, etc...
This is a very important interaction, so you should prepare by carefully thinking about your goals, the plan, your recovery and plans for any period of disability (who is going to help with the kids, etc..), so that you will be ready to ask questions at your preop.