Facebook is the busiest destination for small businesses to get the word out in the world of the Internet--and passed around. There are others. Many businesses get good results using Twitter, Instagram, LinkedIn, Pinterest, and others.
Your marketplace is always changing. Sometimes, the marketplace can throw a gift in your direction. If you are alert, you'll consider whether or not it's right for you. If it fits, grab it and run with it.
Getting started -- Talk with another, non-competing, business owner. Set up an open house at your place or at the other business. Both businesses invite current customers/clients with phone calls, emails, Facebook announcements, Twitter tweets, maybe even a news release. Get the word out to as many people as you can.