I've been in your situation, having started a web design/marketing business 4 years ago, and am now facing the next step in my business...growth. Which is good but it comes with a whole host of new challenges.
My advice is to network and get to know people/build relationships. People do business with whom they know, like & trust. You may be a design/programming wizard that can build sites for anyone/anywhere but to get clients, starting out people are usually going to want to meet with you before committing to having you build/maintain their site for them. Becoming comfortable in front of people and being able to give group presentations is important.
Networking groups I can recommend are BNI, leads groups, and other industry specific groups such as realtor boards, if it's a niche you want to target.
I would also recommend offering more services than just web design/development. That would including hosting, security certificates, maintenance and other skills you may be able to provide such as logo/graphic design, SEO, etc. Don't stretch yourself too thin - stick with your strengths, but I do find it's beneficial for clients and your business if you're not too one dimensional, depending on where your interests and expertise lies.
I wish you all the best. I'd be happy to go over more of my experiences, recommendations, what I'd do differently, etc. in a call.