First, give yourself plenty of time to get to the spa so you don't arrive already stressed out and in a rush. You need a few minutes to check in. This can be quick at a day spa, but take longer at a big resort spa. If everyone gets there ten minutes before their appointment you might find yourself waiting on line and late for your appointment!
Then you need a few minutes to get your locker assignment and change into your robe. Ideally, you should take time to enjoy any facilities like a steam room, sauna, and Jacuzzi. It's nice to take a shower so you feel fresh for your massage. Give yourself a few minutes to relax in the lounge where your therapist will pick you up.
Remember, if you're late for your appointment, it will be cut short. And getting there in plenty of time helps you relax and make the most of your spa experience.