Happy to talk about it! For me it's a side business because there's not enough of it around here to pay the bills. For my partner who's always been a full time mom, it's her only business, but my situation has been rockier than hers.
Basically we're two friends who love to garden and always gave out free advice and our overgrown perennials to friends, who usually killed the plants and ignored the advice. So we figured if we made them pay for it, they'd take us seriously. And voila!
We've both been gardening since at least the early 1970s. I'm from the north, she's from the south, so we both know different sorts of plants. We put ads in the paper, and leafletted neighborhoods, to broadcast about our services. But see, we didn't want to do the backbreaking dirty work -- we do the design and they have to hire the landscapers. So we had to find experts in perennials (who are quite rare) to work in tandem with us. We found a couple of gems who loved our designs and our ideas, and they became our biggest supporters. In fact one of them got so that he refused to do any planting for anyone until they contacted "the girls" as he calls us.
for your blank back yard, I can offer you guidelines. Start with two things: what you love, and what you need. Do you need shade, privacy, erosion control, anti-critter material, lounging space? Do you want color, ease of maintenance, whatever. What plants do you have to have? what do you hate?
Then think of your yard as a pallette, and you're going to paint a 3-D design, like a painting you can walk through that changes with the seasons. Now here's where you need to observe plant habits, and I've never been to Alabama so I'm not quite sure what you've got down there (though my Great Uncle Charlie lived in Bayou LaBatre). You need to know the heights and the needs of the plants. Maybe start small, like a border against the back fence. Don't make it too narrow -- should be at least 6 feet deep, or deeper if you use shrubs. And think of broad areas of color and shape, not single itty-bitty plants.
Hey, I could go on, but I think I hear some snoring...