Start out by adding grass clippings, tree leaves or any other compostable materials. Also you can add ashes to help out. Got a stable near you? Take a trash can at a time over and ask to borrow a can of manure. The more you dig in during the fall and winter the better your soil will be. You can send an 8 ounce sample through your local county extensison agency to a university for testing. They can tell you exactly what you need to add to your soil for optimal growing.