What kind of bird food should you use? The hands-down favorite bird seed is sunflower. It attracts cardinals, woodpeckers, blue jays, goldfinches, purple finches, chickadees, titmice, and nuthatches. Get the black sunflower seeds, sometimes called oil seeds. Birds prefer them to the grey-and-white-striped sunflower seeds sold off the candy rack for people, because they're higher in oil content. They are softer shelled, hence easier to crack open. They're also cheaper than the grey-and-white ones.
Another essential bird seed is niger. Goldfinches adore niger. Niger is a black seed, so tiny and light you can blow away a handful with a gentle breath. Niger is also expensive, over a dollar a pound, so you won't want to waste it. Buy a hanging tube with tiny holes, designed especially for niger, and hang it where you can see it from your best viewing window. Up close to the house, even under the eaves, is fine. Goldfinches will become very tame and won't mind you standing two feet away from them, on the other side of the window, while they eat.