Great tips!
Here's some of mine - Join local groups pertinent to your business, Chamber of Commerce, some artists guilds might accept designers. Be active in those groups and always have business cards/postcards/shirt samples with you. Face-to-face networking may be beneficial if you find the right group. It's worked for me as a freelance artist and my mom, who's a contract trainer.
Also, seriously, public speaking skills. If you have the skills to emcee or present at an event at a convention, that goes a long way. Present seminars and give talks on whatever's connected to your business and put your website on all your (well-designed) hand-outs. These skills also help with phone etiquette and face-to-face networking. Find a good Toastmasters group. Yes, it can be dorky. Yes, some groups suck, which is why I said find a good group :P Participating in Toastmasters is great to develop communication skills and having those skills opens a ton of opportunity and just makes life easier. There are other ways to build these skills, but Toastmasters can be cheap and not time-consuming - bonus, you can use your alotted speach time to make presentations about your business. Example topics like how you became an entrepreneur, where you find inspiration for your designs, et cetera aren't out-and-out sales pitches, can be interesting, and will pique curiosity.
Volunteer, even for just an hour every week, for something related. If you have a sports line, for example, volunteer for an organization which supports a youth team. Pets, volunteer with a rescue. It's a great way to get in touch with your immediate community of potential customers. Of course, no sales pitches, but word will spread or it will enter a conversation.
That's all I can think up of for now. These are all free or fairly cheap, they just take some time. If you use your time wisely, it will pay off.
Run A T-shirt Business On A Shoestring Budget 
