Here are some of the most important points of spa etiquette, according to The Day Spa Association. Arrive at least fifteen minutes early for your appointment,

to give yourself time to check in and get into your robe. If the spa has special facilities like steam or sauna or whirlpool baths, you should arrive even earlier to enjoy them.
You will usually undress completely for massage and body treatments, but your therapist will keep your body draped in dry services and only expose area to be worked upon. Some spas use draping in wet treatments like body scrubs, while others do not. Give the therapist feedback as to your comfort and special troubled areas. You can talk or be quiet, and he she should follow your lead. Relax, enjoy and allow others to care for you.
Understand that you are getting therapeutic massage, which is not a sensual experience. Don't talk loudly in the public areas. Do not bring children and leave them unattended. Gratuities of 15-20% are typical. If the therapist says, "take your time getting up," it means not to get up so fast that you get woozy. You generally have five or so minutes. The room must be prepared for the next client unless she or he says otherwise. Give honest feedback to the therapist, owner, receptionist, etc., as operation personnel cares to know if your spa experiences was as expected.