Good drainage is key.
Worse thing we ever did. And a total waste of money too, Those beds dry out in hours, and the plants suffer from drought. Meanwhile, the rest of the garden can go for weeks without additional water even in the heat of summer, because one good soak in heavy soil keeps the roots cool and moist for weeks. So long as you don't have reasonable drainage, you should be able to grow lots of stuff. Dig down - if you have worms, the soil's can't be too bad.