Select the area you want to improve. If it is wet, let it dry completely before you start working on it. If you take the measurements of the area, it will help you calculate the amount of compost and mulch you are going to need.
Till the soil:
Start by tilling the soil. It will break up the clay. Till to a depth of 12 inches at least to make a difference. Break up all the large clumps into smaller ones because clay soil compacts easily. Till until the soil is loose.
Additions to the soil:
After the soil is loose, it is time to make amendments to it. Add to it the horse, chicken, cow or sheep manure. Till the manure into the soil. Add wood mulch to the soil. You can also add things like grass clippings, dry leaves and fruit and vegetable scraps. Now cover the soil with at least three inches of compost. The compost improves the water retention properties of the soil. Mix in the compost with the soil using the tiller.
After making improvements to soil content, spread a layer of gypsum over the area and then mix it in the soil with the tiller. Look for packet instructions to add gypsum properly to the soil. Gypsum does wonders with soil. It adds in calcium and prevents it from developing a hard crust that makes germination hard for seeds.
After all these additions, make sure that the area is protected from traffic so that the soil does not get compacted from walking over. Placing walking boards along can help people move around without trampling the soil.