I do this, too, and I like it. It's hard work, but there is little to no B.S.
Some tips:
Most houses are pretty dirty at the outset, so figure on taking a little longer for the first couple cleanings. I let my customers know this (of course, I don't tell them it's because their house is so dirty; I just say "it takes me a little while to establish a routine." LOL). I charge by the hour. Most houses take about the same amount of time at each cleaning (once I "establish a routine"

) so the customer generally just leaves the money on the counter, etc. I have some that will occasionally want extra stuff done, like wall-washing or yardwork, and will pay for an extra hour or two, which is fine with me.
I always figured if I charged by the job, some customers probably would try to take advantage of me by tacking on a bunch of extra stuff; or maybe they'd need extra things done, but would feel bad about asking. Charging by the hour makes it much simpler for both of us, IMO.
Have some business cards made (or make them up yourself on your printer) and give them out to your customers. Encourage them to pass them along to any friends who might be looking for a cleaner. I get ALL my jobs through referrals now!
Wear rubber (nitrile) gloves. You can get a box of 100 for like $10 at Wal-Mart. One, they will keep your hands from getting chapped; two, it's much easier to clean glass and other shiny surfaces while wearing gloves; and three, they'll improve your grip. You're much less likely to drop that heirloom vase! Try it and see, it's really true.
Try to use your customers' supplies, but always have your own stuff in the car just in case. Things that are ALWAYS in my tool kit: a bucket, Swiffer duster (the telescopic one) and plenty of mitts, long-handled scrub brush, little sponges that have the abrasive pad on the backside, Tilex Mold & Mildew, Windex, ---- and Span spray cleaner, squeegee, roll of paper towels. Which brings me to my next point ...
Paper towels are your friend! It's much easier to clean with paper towels than rags. I train my customers to leave me a fresh roll, and emphasize the cleanliness aspect, i.e., not spreading germs from one place to another by re-using rags.
Finally, one I learned the HARD way: If a client insists on "green" products being used, increase your rate to make it worth the hassle, as they generally work about as well as warm spit! (I'm sure I'll take some flack for this one.)