Having wisdom teeth surgery in 12 hours. What should I do to prepare and what can I expect?

Follow instructions. If you were given preoperative instructions, follow them. Get a good night of rest before your appointment. If you are to be sedated, follow the instructions given regarding when you are to stop eating and drinking before your appointment. Wear comfortable clothing, flat shoes, and minimal makeup. Take only the meds prescribed or recommended by your surgeon as directed. Bring a driver.
Ice. Applying ice or cold compressed is essential also soft foods, soup, milkshakes etc. Cold will prevent increased swelling. Stay inactive for a few days. You can expect post op pain and swelling which can differ based on the severity of the impactions.
Don't eat. If you are going to have sedation, do not eat 8 hours before the surgery. Expect some level of pain a day or two after surgery.