Match your plants to the amount of light your site receives. Many annuals need full sun -- six or more hours a day. Some, such as impatiens and begonias, do best in the shade.
Consider the balance between good air circulation (which helps prevent disease) and protection from strong winds (which can dry out soil and plants). Cold air accumulates in low spots on chilly spring and fall nights, encouraging frost that can kill tender annuals.
Prepare the soil ahead of time. Poor soil can stunt or kill annual flowers. Do not plant them in poorly drained areas where water pools after heavy rains.
If your site has not been planted before, start improving the soil in the fall before planting annuals the following season. Kill the sod with organic or plastic mulch, herbicide, or by turning it over with a shovel. Hoe out any weeds or grass that survive. The site should be level or gently sloped to keep soil from eroding.
Work in three to six inches of organic matter (such as well-rotted manure) to improve the soil. This is particularly important to improve drainage in heavy clay soils or improve water-holding capacity in sandy soils.
Contact your local Extension office for information about how to test your soil to learn pH and nutrient levels. They may suggest a more complete soil test from the Cornell Nutrient Analysis Lab. Follow the directions on your soil test report about adding lime to increase pH or adding fertilizer to correct nutrient deficiencies.
If deer are a problem at your site, choose plants that deer tend to avoid. Other alternatives include regularly applying deer-feeding deterrents to plants or installing 6- to 8-foot-tall deer fencing or other barriers.