Measure the section of your yard where you want to plant the border. Translate these measurements onto a sheet of graph paper, drawing fences, walls and other permanent landscape features. Use each segment of the graph paper to represent a definite amount of space. For instance, each grid might be a square foot.
Sketch where you want to place the border. Unless you want the border to look highly formal, do not lay it straight. Instead, give it an organic curve. To help you visualize, pretend that a water hose is the edge of your border. Run it along the ground to see how it looks. Note the amount of sunlight that plants will receive in each section of the border.
Research what type of flowers will thrive in your border, given the climate in your region and the amount of light they'll receive in your yard. This information can be found by consulting gardening manuals, horticulturalists and informed staff at a gardening center. Once you know what types of flowers will grow in your border, narrow the selection down to those you find attractive and those that complement the ones you like.
Arrange the flowers on your graph paper. The tallest flowers should go in back, nearest the wall or fence. Medium height flowers go in the middle and short flowers go up front. Clump small and thin flowers together in groups of five to seven, giving mass and consistency to your colors. Run several "drifts" through the border, as well. Drifts are straight or slightly curved rows of a single species, and they help tie the arrangement together.
Prepare the soil. Level the ground if necessary and then add in compost or fertilizer, as per the needs of your plants.
Edge the border with stones, logs or a plastic rim. This both distinguishes the border from the rest of the yard and discourages the soil from running off during storms.
Plant the flowers, ideally by transplanting. If you're sowing seeds, instead, then follow the directions on the back of the seed packet. As seedlings emerge, you'll have to thin them to ensure that they do not crowd other flowers.
Add mulch around the flowers to discourage the growth of weeds. Mulch will also stabilize the temperature of the soil, which will help plants survive the extreme temperatures of winter and summer.