If you select a feeder that does not have some mechanical way of defeating squirrels, how you install the feeder is the key to preventing food theft. If your feeder is on a pole or post, metal or plastic squirrel guards will keep squirrels and even raccoons from climbing the post. Also a plastic shroud over the feeder will keep squirrels from hanging from the top.
What should I feed wild birds? The variety of bird food available in grocery stores and bird specialty shops is mind boggling. Will the wild birds prefer suet, meal worms, sunflower seeds, peanuts or some fancy mix? There's no single answer, but in general the type of food will determine which birds appear at your feeder.
Bird seed is packaged with a single type of seed or many different combinations of seed. Beware of generically labeled "wild bird food" because it may contain a large amount of cheap filler, such as milo, which most birds won't eat. Not only does this waste money, but it is messy. Also, the uneaten seed left in the feeder will mold quickly, which could make birds sick.