Read, read, read. Read reviews of the girls and a few different guy's opinions of the girls. This will give you a good base to work from. Read some more reviews and learn the girls and how the sessions go. Figure out what kind of girl you want to have your session with and go to her or the MP's website and look around and read some more. If she has a profile on a forum, check her out and read what her attitude is like and decide if what you see and what you read is the kind of girl you want.
Make sure you are showered, dressed nicely and that you are polite to all of the girls. Most of them can tell a jerk or an asshole a mile away. You get a lot more mileage being nice to the girls.
Go to the MP of your desires, through the discrete rear entrance and stop at the waiting area, a girl will likely meet you there shortly. (NOTE: We are all nervous/excited, especially the first few times. Somtimes it can be 5 or 10 visits before you get over the jitters of going to an MP, perfecly natural.) Tell her it is your first visit and you would like to meet the girls. You should be able to see any of the girls that are not in a session. Once you are behind a closed door inside the MP, you can pretty much talk freely without fear of the dreaded LE. Chat them up a bit, ask questions and get a sense of their character. Trust me, they know why your are there and there is likely nothing you will say that they have not heard before. Don't be vulgar, but if you have questions ask politely. Listen to how they respond, it will give you clues to how your session is likely to go. Some you will click with, some you won't, one will likely really get your attention. If there are none that you are interested in, thank them for their time and tell them you will be back another day for a session.
If you find one lady you like and you are ok with the sevices they offer and the cost, then tell them what girl you would like to have a session with. If she is not in the room at the time, as long as she is not in a session she will likely be happy to accomodate you. She will offer you a shower, take it even if you just showered 15 minutes ago. She may ask for payment up front for the session and generally speaking that should not be a problem. The girls do get ripped off from time to time, so especially if it is your first time there, they will want the money up front. Once you have paid the piper, nature will run it's natural course. Likely after the shower, she will ask if you want a massage, tell her yes. Lay back, have some fun and enjoy!!
Don't forget to post a review of your session. Remember that because one guy had a really good time in a session does not mean you will have the same experience, it's called YMMV, Your Mileage May Vary. Everyone's experience is different, the better you click with a girl, the better your session is likely to be.