The best training would be to work for a reputable residential cleaning company for at least 6 months, a company that trains you and has good standing in the community. Learn all you can from them. Make sure you leave on good terms as references are a MUST when you go into business for yourself.
Then post an ad on Craigslist under domstic gigs or general labor jobs, or in a local pennysaver or newspaper. Make sure the ad is well-written and succinctly lists your experience and attributes. Don't discuss money in the ad! The best thing to write is "reasonable rate" or "negotiable competitive fee". You may have to wade through a lot of spam but it will be worth the few clients who you sign up.
Then all you have to do is build your reputation. Be on time. Be flexible. Be reliable. Be presentable and cheerful. No drugs, no drama. Treat each client as though they were a family member- provide for your clients the type of service you would want provided to your mother or grandmother.