Assess your yard from a plant's point of view. List all the characteristics of each bed, soil texture, drainage, presence of competing tree roots, rainfall, nearness to a faucet, hours of sunlight daily, and whether the shade is light or dense. Using a pH test kit or meter, find out whether your soil is acid, neutral or alkaline. Determine your United States Department of Agriculture Plant Hardiness Zone. These are based on the lowest winter temperatures a plant would encounter but you also need to consider the amount of heat you get in summer. Fuchsias, for instance, dislike high temperatures while sunflowers and zinnias prefer them.
List flowers that would like the conditions in each bed, using a gardening reference or online source as a research aid. Note whether each one is a perennial or an annual. Each has its advantages and many successful flower gardens include some of each.
Choose a color scheme for each bed. The easiest way is often to divide flowers into warm colors and cool colors, with blues, purples and lemon yellows to blend with everything.
Visit a nursery and look at the plants in bloom. Decide which ones on your list you particularly like and which ones you can cross off. Buy a selection of your favorites.