book thru an agency and never direct..some PS are nut jobs and you do not want them to call or text out of the blue.
You find one that is available, get screened, and see them.
A good place to start is Pamela peaks. She represents a bunch. However in your first email to her, you're going to want yo include all your screening info or she won't respond. There's other sources too. The other guys can let you know. Helpubookher , Adonia, and more. I haven't work the last 2 however.
I've had appointments with about a dozen 'porn stars'. My definition of a porn star is a woman who has done at least 10 scenes and has been around a while. Your definition could be different. Some are/were moderately famous, some just a great time. All of them have been worth the effort.
I'm not in the same tax bracket of some of the folks here so I never go through the big name agencies. I've noticed that some of the same ladies work through other venues in addition to the big name firms - usually at much lower prices.
I find the opportunities by keeping my eyes and ears open to see who is coming to town, or perhaps a nearby town. I then contact them directly. As noted, be prepared to be vetted. 2 other rules of thumb, no deposits and if the verification gets too personal back away; there are extortion rackets out there. Remember Ashley Madison.
Oh, and to restate the obvious; check the reviews.
As my title suggests, I enjoy the hunt almost as much as the event, almost but not quite.
Enjoy the adventure.
directly. I see an ad online somewhere or on TER, mostly, and I send off an email. I've never used an agency. But, an agency is one way to go.
Your best bet, as some others may have mentioned, is to go through an agency for your first few, at least until you get "known". Pick out the star (or stars) that you would be interested in seeing, and then go to the websites for the various agencies, and check out reviews on this site, to narrow down your choice (and get an idea of likely cost), and find an agency (or two) that is representing that girl for private encounters. Then call the agency and make your arrangements. This is usually fairly easy to do after a painless screening.
I mostly use TheLuxuryCompanion run by Adonia. IMO, she's better than the others out there both in the number of ladies represented, and fees and she works hard to make sure the girls show up, and the client has a good time. Pam Peaks (who someone mentioned) is also good - Pam and Adonia both represent some of the same ladies - but Pam requires a deposit IN ADVANCE which is something I object to on principle. Helpubookher I hear is also good but doesn't represent as many ladies as the other two, as far as I know. I've never used that agency although I've talked with them several times.
One word of advice: I recommend calling whichever agency you choose rather than contacting them in email. Email easily gets lost, or forgotten about. And if you contact a busy agency, it's more likely to get lost in the shuffle. It might be difficult to connect by phone, but it's worth it. If nothing else, it lets the agency know that you are serious, and if they want you to send them info in email so they can screen you, they'll be looking for it and it's less likely to get dismissed as a random inquiry from a timewaster.
The bottom line is: decide who you want to see, find out who represents her, go through that agency's screening process, and set up your date. Not really hard at all. The hard part comes later (and if you need me to explain that remark, you're in the wrong place. 
There was a porn star I wanted to meet for a long time and when I noticed they were in NYC, I found Adonia from The Luxury Companion to be very nice & extremely helpful in setting it up! Made my dream come true. I definitely recommend them!
Another agency was less helpful and more difficult, you can PM me if you want more info on that one - that I didn't use.
Just email them directly. You never know. Just be polite. Has worked for me and why pay a middle man (or woman) if you don't have to.
and don't be a dumbass and use your work email account!
As some others have said, an agency is a good place to start, but I would also get pre-screened by RS2K (RoomService2000). This way once you have chosen a lady, and found an agency which represents her the screening process will go that much faster. I would also consider finding out if the lady in question dances somewhere and see her dance. Alternately, you might go to an EXXXotica Expo or the AVN expo and meet the lady before confirming. This will give you some insight as to how she interacts with fans, and if you can get a lap dance how friendly she might be.
Good Luck
Charming Jay
book thru an agency and never direct..some PS are nut jobs and you do not want them to call or text out of the blue.