The question: I have clay soil so heavy you could make ashtrays with it. What can I do about it?
The answer: There is no quick fix, but the best way to improve clay is to fork together one third horticultural sand (it's special gritty stuff) with two thirds compost (or a combination of compost and manure) and mix it into the top of the soil.
The idea is to improve the texture of the soil with lots of organic matter. Doing so will attract worms, which will do an effective job of working the clay into a more manageable loamy mix. If you have really tough clay, excavate several inches down, then add good topsoil (no peat moss or you'll end up with concrete) and finally the above mix. But again, improvement will take time, so be patient.