As ever, Amy’s advice is priceless.
I only do outcalls and will not visit private residences as I prefer the security of a hotel. As you are electing to visit private residences, it is even more vital you do have a safety system in place with a friend. Also, if you are taking advance bookings, I would suggest asking for a deposit as this will cut down on time-wasters and those looking to send you on a wild-goose chase.
Be sure to keep all your things together, and pay attention to how the front door/any doors are locked. Also, if you are offered any beverages, be sure they are from an unopened bottle - have a sealed bottle of water in your bags just incase all drinks have been opened.