Here's the short version of how to prepare for a waxing appointment:
Shower. Please arrive for your appointment clean. I understand some people will have to come in from work or errands, in which case please arrive a few minutes early to clean up with the wipes we have provided in the restroom.
Don't shave. Shaving between waxes almost guarantees you won't get perfect results.
Exfoliate lightly. Use a loofah glove and some body wash and very lightly exfoliate the area you are having waxed the day before your appointment. Really, do this about once a week for best practice, but definitely right before you come in. Be gentle.
Mentally prepare. Try and get a good night's sleep, don't drink a ton of coffee the day of your appointment, DO drink a ton of water, and if you're having a rough day, try and calm down. Your mental state can really affect your experience/pain threshold.
Hang in there! The first time hurts the worst. It gets WAY better after that. You'll love me next time around! :)