Oh, clay soil is nasty to work in, cold in the spring, slick and slippery when wet, hard as a rock when it dries out. I know, that's what we have. Best suggestion, mulch it heavily with whatever leafy, green material you can. By heavily, I mean at least 4 to 6 inches deep. Add some earthworms (you can buy these at many gardening centers, over the internet, or, if need be, the local bait shop) and plant what you can in it. Plants will grow it in and grow well, but not as well as in rich, friable soil. Mulch and worms will help a lot, but it will take time and some rototilling the mulch in at the end of the season (renew the mulch as it rots down through the season--we use the clippings from mowing our lawns) does help it tremendously.