Your first step is getting licensed and insured. The insurance is going to be mandatory, not just a nice idea because if you accidentally ruin a customers carpet, or use a a toxic chemical in your cleaning supplies that makes your customers sick, then you must pay the damages.
As for screening customers? How do you intend to get customers, what are you going to do to find them? If you are going to do residential cleaning, decide the neighborhood or types of residences you want to clean. Cleaning a fifteen room house is very different than a one bedroom apartment.
It appears you are going to wait for people to call you instead of going out knocking on doors. First thing to ask yourself, why would they call you when there are franchises that have been in business longer, have the proper insurance, equipment, bonding of their employees and contracts stating how much the customer will pay? Have you looked around to see what those large franchise's are doing that you can do better or do you know what they offer or how they get customers?
As for personal safety, doing the above steps to find customers will help with that. If the neighborhood or area looks shady, don't put flyers or knock on doors there. There are no guarantees when going into someone's home that you will be safe, no matter how good the neighborhood. Whether you are willing to risk it or not is something you have to decide.
Have you cleaned someone's residence before? Friends, neighbors, etc. How long did it take you and what did you do, who owned the vacuum, brooms, mops, cleaning cloths, etc.? How did you get there and how many did you clean? Try cleaning for at least 5 other people before you start. That will give you an idea of how long it takes to do certain tasks and if there are those that you don't want to do, like windows or stairs or when the family is at home or if they have pets.