Poor drainage is one of the most common causes of fruit tree failure.
To test your drainage, dig a hole about one foot deep and fill it with water. If the water drains within three or four hours, fill the hole again. If it takes longer than three or four hours to drain on the first or second filling, you have poor drainage.
Where soil drainage is poor, you can either 1) avoid planting there, 2) plant above the present grade by constructing a berm or raised bed, or 3) construct a French Drain, a trench filled with gravel or rock that allows water to drain away from the planting area.
For more information about planting fruit trees, see Planting Your Backyard Orchard.