Habitat is a bird's neighborhood, and like any neighborhood, certain residents turn up reliably and others almost never do. A marsh bird generally isn't going to appear in a mature forest interior. A woodpecker needs standing trees. Many sparrows favor brushy edges over open lawn or deep woods. Just noticing where you're standing rules out a large chunk of the field guide before you think about anything else. This also explains why a familiar species can look wrong out of context. A bird you know well from your own yard can genuinely stump you the first time you see it somewhere unfamiliar. Has habitat ever helped you crack an ID, or thrown you off because a bird showed up somewhere you didn't expect?