This is a really good question, I wish I knew the answer to! I run a very small business, while also working full-time. While I would like to get more business, I'm also afraid of having too much and not being able to handle it!
I think a lot depends on the nature of the business. You want to "target" your potential clients. For example, I do business almost exclusively with attorneys. So I should look towards the local Bar Association website/magazine/newsletter to place my ads. However, my work is usually limited to certain types of lawyers. It would do me no good for corporate lawyers to see my ads. So, I might want to look for organizations that practice particular types of law, such as Criminal Defense or Employment Law. That would be a wiser move. Once you figure out who you are trying to target, you figure out how to target them. Ideally, you would seek out free publicity, perhaps through strategic posts on LinkedIn or Facebook. You could mail out flyers, but that could get expensive.
You would want to look and see if your community has a Small Business dept. San Antonio does, and they teach people how to run a small business. It's important to learn as much as you can before you get started! Congrats on planning ahead!