I suppose this could apply to anyone of our platforms but I find it really applies to responsive websites since there's so much competition.
I preach that the best course of action is to find a niche you are comfortable with and look at many sites in that niche and find out what they need from their website and how you can best provide it. By positioning yourself as a website expert in a particular niche it gives you the ability to charge more by providing premium services compared to freelancers or agencies that do not have a particular focus.
By being able to provide a niche focus along with hosting, domain management, analytics, updates, maintenance and SEO you can charge a monthly fee in addition to design and setup. Let's say you can land 24 clients in a year, you charge $1,200 to design and create a site ($28,800) and you charge (since you are the expert in that niche) $299 a month ($86,112) that is $114, 912 for the year and an ongoing $86,112 yearly. That is assuming only 2 clients per month!
Obviously not every type of business will be willing to pay $299/month for their website so focus on a niche that you know is profitable where you see the potential in say many with older websites. Even at $149/month to match the totals above you would only need to get 4 clients a month.
Once you have done this successfully for a few sites there is no need to reinvent the wheel. You can than branch out to other similar industries or expand your geographic reach with very little issue.
I'd be interested to hear how you are doing. Do you have a focus? What industries do you serve?