First, you might want to have a soil test done. This will give you an idea of nutrient levels, pH and organic matter content. Recommendations for improving your soil are included with the results. Contact your Cooperative Extension Service for information or purchase a test kit at a garden center.
Turn over the soil—either by hand or with a tiller—as early as possible in the spring. Just wait until the soil has dried out so it doesn’t form big clumps. Tilling wet soil will compact it too much and can do permanent damage to its structure. Let the tilled garden sit for a few weeks, and till again. This will take care of any newly sprouted weeds.
It’s always a good idea to add organic matter to any garden soil. Organic matter improves drainage on clay soils, and helps water-holding capacity on sandy soils. Compost is best, but shredded leaves, grass clippings, well-rotted manure or other organic matter can be incorporated directly into the soil when you first turn it over in the spring. Wait a few weeks to plant if you use non-composted additions.
Then throughout the season, use a 2-3 inch layer of mulch (compost, shredded leaves, straw) on the soil to keep down weeds, retain moisture and add even more organic matter.