Before we planted my Mom and Dad's garden last Sunday, we double dug it. My dad gave us instructions. (I had already spread a good 4 inches of new compost on the garden.)
First we dug a 12 inch trench and moved all the dirt to the far end of the garden. (We I say "we dug" here, I will mostly mean "my husband dug".) Then we turned the adjacent soil into the trench to progressively move the trench down the garden. The result is a bed loosened and amended 12 inches with minimally disturbed "structure", which means happy worms and other soil inhabitants.
The bottom layer was dense and very hard to dig. I hope this year's vegetables will benefit from this nice preparation. It took about 2 hours for the 3 of us. A good team project.