First, start with fluffy/healthy soil. If you can't scoop the soil up with your hand having it fall apart freely then it's time to add product to beak the soil apart. Adding compost is the best way to get your soil fluffy and healthy. Compost is decaying material that, when mixed with soil, will bind to the soil matter and keep it from hardening up. Compost decays slowly in the soil and feeds plants throughout the summer, resulting in less need to add fertilizer during the growing season. Compost also holds onto moisture keeping soil wetter longer. Adding compost to your garden every spring will keep your soil healthy. The best compost you can get is made by you! But, when buying compost you get what you pay for, so think about spending a bit more to get better quality compost. There are no regulations on materials used for compost/soil, so cheap compost most likely will contain plant matter that was sprayed with chemicals when it was alive.
Second, buying plants locally grown will give your garden a head start. Big box stores ship plants in from warmer locations, and the plants have to adjust to the local climate. Plant tags from big box stores often describe care for warmer climates and not that of places where it freezes, so pay careful attention to both the source and the included care instructions.
Thanks to Robert Leisz with Nature's Gallery for writing this article. Feel free to stop in the store or call with any questions. Nature's Gallery, 4901 Lowell Blvd., Denver CO 80221. 303-668-0347.