It is customary to remove your clothes and they usually provide a towel on the table. Then lay down on your stomach and drape the towel over your butt. Of course, it is very advisable to come to the spa cleanly showered and smelling good. If you are coming directly from work see if they have a shower and take a quick one. There is nothing more off putting than a client who smells bad.
Generally ( if you are seeing someone first time ) half hour is good time. They will usually do full body massage for about 20 minutes and will leave about 10 minutes for fun stuff. At the point of the flip over some attendants change from massage to doing a finger tease...all over your body and bum area. This is a sign that fun stuff is to happen next. The mpa may ask you what extras do you want? This will evolve based on your experience. A body slide is customary. Hand Job should be included as a minimum. Don't expect full service unless the place is specific for that. Always make sure you and her agree to the price of the extra. It can range and differ ( sometimes alot) depending on the mpa and her extras being provided.
Generally advice is go with the flow, don't be afraid to ask questions. Be respectful. You can feel the mood out, explore, she will let you know her boundaries. Never be pushy or creepy. Respect of the MPAs will get you the best value for your $. Also, try not to fall in love. Remember, it's a job for her. The pros make you feel special and that you're the only one. Just enjoy that feeling but remember where you are.
Happy Hobbying and enjoy