You can prepare a planting bed for beans wherever the soil is workable.
Pole and runner beans and lima and broad beans will grow well in soil too poor for most other vegetables. But soil enriched with aged compost and fertilizer will give beans a good home to grow quickly and yield well.
Bean planting site. Choose a spot that gets full sun throughout the spring and summer, is out of the reach of a constant breeze, and drains well. It is best not to grow beans in the same ground within 2 or 3 years as diseases are likely to harbor in bean refuse. But if you have few alternative growing spots and there was no disease in that spot this past season you can plant again in the same spot once the soil has been enriched.
Preparing the planting bed. Dig a trench 18 inches wide and about 12 inches deep. Loosen the soil with a garden fork then add a 3 to 4 inch layer of aged manure or compost to the bottom of the trench. You also can add bone meal or hoof and horn fertilizer (which improves root growth and soil structure) or blood meal (which contains slow-release nitrogen for green growth). Then fill the trench with 3 to 4 inches of soil and a second layer of compost and then the remaining soil. You will now have a planting bed or row slightly raised above the surrounding garden ground—it will be quick drain (beans like well-drained soil) and quick to warm in spring (ensuring rapid seed germination).
Mark the trench with pegs or garden flags. The planting bed is now ready for sowing beans late next spring.
Time to plant. Bush and snap beans can be planted after the danger of frost is past in spring, say 2 or 3 weeks after average date of last killing frost. (They will not withstand frost after they are above ground.)
Windsor or Broad beans can be planted as soon as the danger of hard frost is past and the soil is dry enough to work.
Lima beans are hot-weather, long-season beans so it is best to plant them well after all danger of frost has past.
More tips at How to Grow Beans.