Here are the steps to building a new bed or border from scratch.
Keep the lawn from crawling into your garden with a good edge. A trench about 8 inches deep and a couple of inches wide will stop even the worst invaders from crossing. Alternatively, sink an edging material around the perimeter of your garden.
Though it takes a little extra time, placing all your plants before you put them in the ground can make a world of difference. This allows you to get the spacing just right and make your plants really will look good next to each other.
When you know all of your plants are in exactly the right spots, plant them in the ground. It's helpful to loosen or tease the plants' roots before you put them in the ground, especially if they were rootbound.
Other than amending the soil, the best thing you can do to keep your new garden healthy and low-maintenance is to spread mulch. A 2-inch-deep layer of shredded wood or other material will do wonders for stopping weeds and helping your soil conserve moisture during times of drought.