There are several variations but you can narrow it down to four key components. Food. Water. Shelter. Space.
Food: Simple enough. Throw some birdseed out right? Absolutely nothing wrong with a little birdseed as long as you have a balance of plants, insects, lizards, etc for your birds to choose from as well. Butterflies and native bees like a variety of flower shapes and colors for nectar. You want to make sure that if you supplement with seed or feeders you have a variety of native natural sources such as grasses, flowers, and berries available as well.
Water: While this is the most overlooked, this doesn’t have to be a big complicated pond. Butterflies drink from puddles in the sand. You can make a basin and use a drip emitter to fill it when your irrigation comes on for a small watering hole. Birdbaths work for more than birds. Using natural mulch keeps moisture readily available for lizards and insects. It’s important for all wildlife to have access to water for bathing and drinking year-round.
Shelter: This is protection against the weather, a safe roost, and a nesting area to raise their young. For insects, this is leaf litter. (don’t forget you NEED those insects for the prettier wildlife) For almost everyone else this is going to be grasses, shrubs, trees, that kind of thing. This is where natural pruning comes into play as well. If that Texas Ranger is pruned into a geometric shape it is not much use as a shelter or a food source. Rock piles look very natural in our landscapes and are excellent shelters for a wide variety of wildlife.
Space: This is also referred to as Cover. It’s the idea that wildlife has access to forage, seek cover from predators, protect their young, and have access to diverse conditions. You can provide all of these things even in a limited amount of space. A yard that is cacti and gravel would not be able to provide this. There is no diversity. Now add a few nectar plants, a shrub, and maybe a tree and you have the makings of a wildlife habitat.