I really like all the comments here. They're all good!
Me, I did a lot of research and bought the least expensive commercial grade 4k psi, 4 gpm unit I could find, strapped it down in the back of my pick up, and went to work. In my neck of the woods (literally, woods), there's a lot of poultry farms, and they need regular washing. That got me started. Bought a subscription to The Cleaner Times, and read every word. I went to a round table, joined the cleaning assn. that sponsored it, and got certified in house washing, and kept reading. Bought Quickbooks by Intuit, and found that Intuit has simple websites for less than $10 a month. Got a web site. Went to PWNA convention and got certified in wood restoration. Learned how to get web site on 1st page on search engines. Getting more jobs. Went to Vista Print and designed my own business card for cheap. Put a whole bunch out. Got a whole bunch more jobs. Now I have my old machine, and a 3500 psi, 8 gpm hot water unit that allows me to do just about any job that I come across. And on and on.
Here's the real kicker. I found out right off the bat, provide the service, do a real good and thorough job, and always, always, always, find something you can do for your customer that you don't charge them for. It'll be something that doesn't take much of my time, but stands out to the customer.
So, know your business, do it well, do it for a reasonable price, and do something for free. You'll hook 'em every time!