If you have a shady area, first determine how much shade it actually gets. Watch it and document it over the course of a sunny day-remember the light will change come summer so keep that in mind. Is your shade dappled, or is it full shade? The trickiest shade to deal with is the often confusing "part shade." It doesn't have to be. Just make sure you know when and where hot sun hits. You'll want to know which areas get hot afternoon sun because this is the exposure that could potentially burn the leaves of shade plants esp in the summer.
Next, buy a good shade plant book for your region. There are a gazillion. Better yet, go to a trusted nursery that has a good shade plant selection. Don't forget shade loving natives.
Think about what you would like out of your shady spot and design from there. Do you want a cool seating area? If so, build around that. Do you want a serene moss and fern garden where you can pray for thinner hips? Get the moss going now since it takes some time to establish and keep it nice and moist. How about a secret garden where you can hide from the tax collectors? Or a mysterious woodland garden with a winding path. If so, get the larger shrubs going like japanese acuba, fatsia japonica, or a shade loving hydrangea.
Something else to think about while planting in the shade-if you want a little burst of light, consider plants with light green foliage, variegated foliage, or light-colored flowers. Some shade perennials I like are native columbine, brunnera, astilbe, lily of the valley, sweet woodruff, maidenhair ferns (and others), bleeding heart, lady's mantle, ajuga, and foxglove.