After tilling the soil, perform a soil test to determine the health of your soil, including its nutrients needs. You can purchase a soil test from a garden center or contact your local extension office for a low-cost soil analysis that's usually enexpensive. Most soil tests require you to take samples from several different areas of the soil. Mix the samples together and use a small sample for testing. The test can determine the pH of your soil and may recommend specific amendments to use.
After you have the soil test in hand, determine what amendments to add to your soil. You want to aim for a neutral pH. Apply lime for a low pH and sulfur to counteract a high pH. Most soils benefit from a 2-inch layer of compost, or more. The compost provides a wealth of nutrients to make any soil type healthier, and can help loosen the soil.
Once the amendments are added, re-till the soil to sufficiently add the amendments into the soil. Work down to a depth of at least 6 to 8 inches to completely incorporate the amendments. If the amendments are not completely mixed into the soil, they won't be as effective and may interfere with root growth.
Smooth out the the top of the soil after tilling with a rake. Amendments may take several seasons to completely change the soil texture; give it time to see significant results. The National Gardening Association recommends adding a cover crop when the gardening season ends to help improve the soil's health; their recommendation for what cover crop to use varies by region. In the spring, you can till the crop back into the soil.