I have been in business mowing for 6 or 7 years now. Craigslist is how I got my start. Havent expanded much beyond that. I do have a facebook page, but dont get much from that. 99% of the time a customer calls they say "I saw your ad on craigslist".
I dont have facebook, but my wife does and she set it up and is always "promoting" it and uploading new pics all the time of jobs. But I if the average customer is like my wife, that has hundreds of friends, following hundreds of pages....you can post a pic and 15 minutes later....you would have to scroll down forever even to see it.
I do have a business name, tax ID#, business cards too. Alot of my business is word of mouth. And it also helps that a close long time friend of mine owns one of the larger mowing/landscape/irrigation services in the area. He subs me out for the bush work, and sometimes just gives them my info rather than sub me.
The issue you are going to have, is at some point you are going to need to decide if you want this to be a legitimate business. Licensing and insurance and all. I do a fair amount of commercial work, and the average yuppie on craigslist with a tractor and mower working for beer money aint gonna set foot on those properties.
And its really hard to justify charging premium price as the big dogs in the area are, if you arent a legitimate business, insured, etc. So are you going to be a bottom feeder under cutting they guys that are legit trying to run a business? What happens to all of your customers once you decide to go legit and get insurance and have to start charging alot more to cover your overhead? How many customers are going to start giving you a bad name because last year you mowed their field for $80 and now you have to charge $150 since you are a legitimate business now?
Craigslist is a good place to start for sure. But do quality work for a reasonable price and your name will spread through word of mouth.
But as I said, decide if you want to do this the right way as a business with insurance, or if you want to be one of "those" guys that risk everything they own for beer money.