Much of my garden is solid clay - as in you could put a chunk on a potters wheel and throw a pot. There used to be a brick factory on our road. Anyway, we did mulch twice when we moved in, first with wood chippings from the arborist and again in the fall with dead leaves, but that's really only made a thin layer of soil on top of the clay.

I've had the most luck with trench composting. Any time I plant something, I dig a deeper hole than I need, put food scraps, used paper towels, or whatever composting materials I have in the bottom, and plant on top. If I have extra compost material, I dig a trench and bury it wherever I'm next planning to plant. Within a few weeks everything except the eggshells and other stubborn materials have disappeared into the soil.

The ground has improved immensely already. We've been here two years and this year when I went to plant my onion starts I was amazed when I turned over dark crumbly soil with a hand trowel! I've had some lovely produce from my garden last year, too.

Of course if you can afford the time and/or money to get truckloads of compost in and spread it or till it in, that will improve your soil immensely. But you can also do it a piece at a time with materials you already have and end up with some really beautiful soil.