Till soil to at least a foot deep before planting. This allows better drainage beneath the roots; otherwise, soil compaction may prevent aeration and allow fungi to proliferate in the soil. Add sand or peat moss to heavy soils to create better drainage -- how much you'll need to add depends on your soil.
Buy bean seeds pretreated with a fungicide and plant them only after the soil has warmed to at least 65 degrees Fahrenheit.
Keep bean plants well spaced, following the package recommendations. Avoid applying nitrogen fertilizers at the time of planting.
Keep your bean plants healthy by watering them enough to keep the soil moist; however, do not allow the plants to sit in puddles of water.
Remove and discard plant debris from the area after harvest. Rotate crops so you do not plant beans in the same area for more than three years in a row.