I have also used a product called Earth's Fortune that is volcano ash. This adds nutrients and minerals that are often lacking in my sandy soil. Now clay is a different story I feel it is a greater challenge to deal with than sand. Covering the clay with leaves, grass clippings, manure, wood chips, and lots of green debris and then tilling them in will help. Stony mixes, not fine sand might help a little also.
All soil needs organic matter.
Just think about how soils are replenished in nature. Leaves, grass, dead insects, and animal droppings all are constantly put back into soil. This is a necessary and natural process. When we rake leaves, pick up grass clippings to bag and maintain an otherwise sterile garden our soil becomes stale and then dead. So remember, good common sense, do as nature does, let your soil live and be healthy and your plants will thank you.