1) Learn and leave established native flora undisturbed.2) Remove invasive species and then wait to see if native plants begin to grow without assistance. (When native plants start on their own, then these plants or trees are likely the most appropriate flora for the habitat.)3) Scatter seeds from nearby native plants in a similar habitat.4) If you feel you must add a new plant then select a native plant while considering how the plant fits with the specific habitat and understanding the plant's logical place in the normal succession of native plants.
My friend Elaine Chuang shared several resources (that were new to me) from the January Washington Ornithological Society meeting. The major new concept is that specific keystone native plants enable critical moths and caterpillars that in turn provide food for the great majority of birds, especially during the breeding season. Here are the top two links from her list.
Native Keystone Plants for Wildlife:
Resources for adding plants to your Pacific Northwest Garden:
Click Here to access a King County publication that explains the best placement for a wide variety of native plants. It looks quite helpful.
Also, Jane Lundin has created a small package, with a lot of critical information that looks quite handy, and light, for backpacking in the mountains in Springtime. It is titled, Mountain Wildflowers of Washington.)