The first thing is to define WHO your market is, and then determine where they are, or what they like to do. Social media can be a great resource if you're in the right group and share the right information.
If you can DOMINATE a niche, you'll have no issues with finding clients. For example, if your hobby is model airplanes, you'll be active on those forums and available for when someone has questions about a website etc. If they allow banner ads/newsletter ads, create them with your username in full view so they know you're active on their forum also.
For me, I dominated the "about.com" forums when it came to design, and HTML help. From there, my HELP to people became known and our company expanded quickly. It only took about 2 years, but my company was the default recommended and we hosted nearly 300 of their forum members as a result.
Marketing 101: Big Fish In A Small Pond!
If there's a particular software your users use, optimize it, get involved with those forums and then dominate it. We did that with an e-commerce software and we were the main recommended company with over 1500 of their members using our servers.
So, first, figure out who your target market is, then figure out how you might be able to help them, and THEN figure out the marketing.
@Artashes will attest to the hosting of these forums with our company, and again, a big reason was that we provided support to EVERYONE on the forums, and for our return on investment of time, we had a number of forum members on our network.