Here are the basics of a Wildlife-Friendly Garden:
Food. Planting native plants is the easiest way to provide the nectar, leafs, seeds, and nuts local wildlife needs. You can also supplement with elements like squirrel and bird feeders.
Water. Wildlife needs clean water to drink and bathe. If you are not near a natural water source such as a pond, lake, or wetlands, you can provide an artificial one like a bird bath, puddling areas (for butterflies), or rain garden.
Shelter. Wildlife needs a place to hide from people, predators, and bad weather. Little critters also need a place to raise offspring. Dense shrubs, thicket, rock piles, and birdhouses are a few options for shelters you can include in your wildlife habitat.
Keeping it green. Using Green Gardening practices will keep soil, air, and water clean and safe for local wildlife (not to mention you and your family).
Once you have these basic elements of a wildlife habitat, you can apply to be part of the National Wildlife Federation's Certified Wildlife Habitat program. For $20 you get a personalized certificate, a one-year subscription to National Wildlife magazine, 10% off all NWF catalog merchandise, a subscription to Wildlife Online — Habitats (a quarterly gardening and wildlife e-newsletter), an optional press release for your local newspaper announcing your certification, your name listed in NWF's registry of certified habitats, and the opportunity to purchase a Certified Wildlife Habitat yard sign (see picture below).