Clean, convenient, safe, discreet, parking.  And definitely the boobs inside!!  

I agree with Wingman: "Clean, convenient, safe, discreet, parking."

I'd add: Picked up.  So's I don't have to step over laundry on the floor, McDonald's bags behind the couch, hair in the shower, etc., etc.  I've had a couple of those, and they're definite turn-offs.

I typically prefer a more 'busy' location so I don't draw attention.

It helps the fantasy if it feels like your hideaway, not your incall. Like you're about to finally about invite me to "your place" and you've cleaned up the place in anticipation. Like you want things to go just right with no distractions. Maybe a tall order, but you asked!

.... discretion/privacy without it being too hard to find. So yeah pretty much what you'd look for @ Arcana  something discreet but convenient. Affordable is important but if the location is great and convenient for most dates and therefore maximum $$$ for you then affordability in the end might not be such a big deal.

Nice, convenient, beautiful one-bedroom w/ balcony & pool located in the center of the city.

Assuming that you are talking about a multi-unit residential type property, then the primary consideration, and not to dismiss the others that have been mentioned, is that your visitors will ne able to come and go inconspicuously without raising the eyebrows of nosy neighbors. Whether you plan to entertain during the day or evenings will be a big factor. I have visited nice apts in the warehouse district where there were two providers sharing one place but only used it during weekdays and also only during the day.  It was not a building nor location that appealed to families and most other tenants were gone during the day so it worked well. Had they entertained in the evening, it might have been ackward. Entrances from the interior are best because your guest will not be conspicuous entering a main entrance of a multi-unit property and traffic coming and going isnt easily associated with your unit.  You will want to inquire about the types of people you will have as neighbors in the units neighboring yours.  Somehow, you also need to determine how sound proof it is, lol.

Nosy neighbors can be a major source of trouble. I have known several providers who have learned that the hard way, one of which created some heartburn for me in the process. As a result, I prefer to see only very low volume prividers with private incalls, and then only when the unit can be accessed very inconspicuously.

Being able to come and go without my exact destination being easily observed by the staff and/or other residents is most important.  Safety is also important but it is relatively easy to figure out if an incall location is in a bad part of town.  Convenience is not as easy to figure out because it is different for other people; a location close to me is obviously more convenient for me but is less convenient for some others. I also like easy and free parking (pay parking is a pet peeve of mine).