SEO, SEO, SEO.....
I work as a designer/pre-press guy at a digital and wideformat printing company in the North of England.
In the past 3 years, we have gone from 3 people to 10 people and continue to grow - all during a recession - so I think I know a little about all this, although it may not translate directly to your business.
We have done so much to get more work in, and in conjunction with our website (see my sig), SEO has given us by far the greatest return. By FAR.
Type 'banner' into Google - we are #1 I believe. Getting good search terms into the top 2 or three results has proved to be the dealmaker for us - the traffic to our site has gone through the roof. We have also done extensive usability testing on the website too, to convert as much of the visits into sales as possible. Pound for pound, this has easily beaten all the email and mail marketing (all professionally designed - not by me!) and social media up the wazoo.
Now, I agree with most of what has been said above - face to face is always best if possible. As a designer, you are pretty much selling yourself, but I guess you know that already. But then again, graphic design is one of the few businesses that you can do entirely over the internet (I'm dreaming of a poolside position, somewhere in Thailand....) so you may as well push the internet as a stream of income. There are only so many hours in a day for visiting clients, but your website can be working for you 24/7/365.
As a website designer, I'm not sure of how much of the following you already know, but:
Google sees your site in many ways, and I'm not an expert on this, but the quality of the content (including keywords) is one part of the puzzle. Another part of the puzzle is reputation, and this comes from having links to your site from other places, and i believe that this is one area where you can make a difference without getting too into things. There are several people on eBay selling backlinks - check out their feedback, find a good one, and spend your money. A guy I know got to the top of google for leaflets this way - just buying random backlink packages. It may well work for you.
The other way, and what we did, was to enlist the help of a dedicated SEO company and pay them a monthly fee for a years worth of work. They did all the linking, helped us sort out content (in very specific ways) are recommended many ways in which we could help the whole situation. You can set a monthly budget and go from there.
After 2-3 months, you could easily find yourself in the top few results in Google for 'graphic design', or whatever keywords you choose.
All for now, Kirk out....
Jim