All flowers go together; some just get along better than others. Ideally, keep flowers that have the same lighting, watering and soil requirements together. Combine flowers so that there are blooms from early spring to fall so your garden always has some color. Combine colors, plant heights and growing habits for interest.
Sun or Shade Lovers
Flowers like artemisia, zinnia, cosmos, penstemon and coreopsis love the sun and do well in beds that are in the sun all day long. Pansies, snapdragons, helleborus, begonia and impatiens do much better in shady beds. Sun lovers will make do in partial shade but the opposite isn't true. Shade lovers tend to crisp up when exposed to too much sun. The angle of the sun changes from spring to fall, which changes the shade and sun patterns in the yard as well.
Flowers All Season Long
Plant the garden with varieties that will give you flowers all season long. Snowdrops, daffodils, primrose and crocus provide early spring color. Mid spring brings tulips, alyssum, violas and snapdragons into flower. Early summer is the time roses start to bloom and they continue right through the summer. Mid summer sees daisies, marigold, yarrow and hollyhock blooming. Late summer and early fall brings out chrysanthemums, sunflowers and asters. Plant a variety of flowers that will keep your garden decked out in color from snow melt to the first frost.
Combining the right colors can bring a restful ambiance to your garden through pastels and white flowers or a burst of energy through a riot of colors from the use of blues, reds and yellows. What doesn't work is to have a hodgepodge of everything without a color scheme in place. Light pinks, blues and purples of Larkspur would look odd with orange poppies for examples but just right with a pop of yellow calendulas. The sweet white clouds of gypsophila would get lost in a garden with vibrant yellow, oranges and reds of zinnias. Colors can also be used to make a garden bed recede or look closer. Reds and oranges seem to be closer than they really are, while blues and violets look farther away.
Height and Habits
A flower bed all the same height, size of flowers and growing habits is boring. Contrast the sizes of the flowers from tiny Texas bluebells to hibiscus by clustering the Texas bluebells in a mass. Shorter flowers like lobelia and marigolds make a nice edging for taller flowers like oriental lilies, dahlias and flowering tobacco and won't be hidden by them if they're in the front of the bed.