Work with the soil when it's relatively dry. Choose moderately warm days when soil is loose and warm. If you're planting new vegetables, flowers, roses, shrubs or trees, start your process after the last frost in spring.
Break up the top 12 inches of natural soil, using a garden fork and spade. This loosening creates better internal drainage. Mix 3 inches of organic mulch like wood ships, straw, bark or grass clippings into the tilled soil, then add 3 inches of organic compost. These amendments create drainage through the soil, build up the soil level to create drainage around the site and add nutrition and moisture retention for future plantings.
Re-amend soil periodically, as mulch and compost break down over time. Treat the soil again in fall before winter arrives and lay mulch over the soil to protect it through the winter. Re-amend soil again in spring before any new plantings. Add mulch and compost to established plantings to maintain soil quality and facilitate drainage.