Thanks for writing! The best way to improve any kind of soil is by adding organic matter, such as compost. Incorporate as much as you can find to start out; this will help push those tiny clay particles apart, and also encourage beneficial organisms like worms to help keep naturally working the soil for you.
You may be able to find large quantities of organic matter available in your area or little or no charge. For exmaple, many munincipalities offer free compost piles for residents. Or contact local tree trimmers and see if you can get some of their sawdust and mix that with well-rotted manure to start your own compost.
---Justin, Senior Garden Editor, BHG.com