The best amendment is organic matter, like compost. Applying 2 to 4 inches over the area and tilling it evenly into the soil will help improve the soil conditions. If it is really heavy clay and amending the soil does not seem to work, building raised beds may be more beneficial in the long run. Cover crops can also assist in loosening up the clay. Here are a couple fact sheets and a publication that may help. For additional assistance contact the Logan County OSU Extension Center - https://extension.okstate.edu/county/logan/.

Healthy Garden Soils, Raised Bed Gardening

Oklahoma Homeowner's Handbook for Soil and Nutrient Management