Miracle Grow is good, but it has it's limits. It won't make your soil any better. Assuming that the soil has never been tilled or used as a garden (even if it has) it might be best to add peat moss, well rotted manure, and after checking the Ph (check your local garden center to see who does this in your area) perhaps some other soil amendments. If you have a compost pile and the compost is well rotted, use that, too. It's among the best things you can add. If you don't have a compost pile (or bin) plan on starting one. The things listed above are natural, not chemical...and if you can stay away from the chemicals until all else fails, that would be best.
In order to get this stuff mixed in with the existing soil, get yourself a rear tine tiller (even if you have to rent it for a day). It will make mixing the ingredients together much easier.
One more thing, if your soil is very heavy and clayey, then add some coarse sand. Spread about an inch or so on top of the entire area your working, and just till it in. It will help to keep the soil loose.
[This message has been edited by treebeard (edited April 23, 2003).]