Select the site where the new bed will be located. Pay attention to such key elements as sunlight, surrounding structures and trees that may block the sun, as well as underground utility lines. Phone 811, a national, free service that locates underground lines for you, or have your utility company send a crew to come out and do a locate.
Make a sketch. It's a good idea to do this to scale, and graph paper is the easiest way to get an accurate idea of the size of the bed you plan to create. When you're sketching, include surrounding structures and think about which plants you want to include and their size at maturity: Will they fit in the space provided? This is especially important if you decide on a raised bed, which tends to contain plants and keep them from sprawling beyond the borders of the bed.
Outline the shape of the flower bed on your chosen location using a garden hose.
Remove the grass. There are two approaches to achieve this: Lift the grass from its place, or smother it where it grows. For the first method, use a flat shovel and dig around the perimeter of the site, then dig in the center of the spot. Lift the sod from the ground, shaking the earth free from the grass as you remove it. Till the earth underneath the sod and incorporate a few inches of compost to add nutrients and loosen the soil. If you'd rather smother the grass, cover it with layers of newspaper, paper bags or cardboard. Water the layers well and cover them with 6 inches of compost. This method works best when you have a season or two to let the paper decompose.
Define the edges of the bed. You can do this using large rocks, bricks, a gravel or straw border, or a thick edge filled with bedding plants. Whatever you find attractive in your garden will work. If you decide on a raised bed, you'll want to tamp down the edges and make sure they're level before you add the border.