Bluebirds are wonderful little creatures, and a pure joy to have around. The Eastern Bluebird is the common variety in my neck of the woods, and I try to accommodate them the best I can. Feeding them is important, but in order to entice them to hang around, they need dwellings.
Gourds make good bird houses for bluebirds, if you don't want to showcase your carpentry skills. Just be sure and hang them so the rain doesn't blow in, and make sure you include drainage holes in case it does. I grew a truckload of gourds one year and with the help of my young niece made dozens of bluebird houses.
Bluebird houses need to be six feet up off the ground. They may be a little lower, but not much. The birds will not build in houses much out of this range. And you need to be able to access the house for cleaning at the end of the season, plus you want to be able to watch these rare beauties.
They will build in houses attached to trees, but seem to prefer the ones on poles. If you are building your own house, do not, I repeat DO NOT make the access hole larger than one and one half inches in diameter. If you do, you WILL find your baby bluebirds murdered by starlings. These winged devils spend their days on the prowl for nestling's.
Bluebirds don't eat much seed, they are mainly insectivores, and the way to attract them is with mealworm feeders. Mealworms are expensive, but if you are seeing bluebirds around your property already, half the work is done. You may only need to supplement the natural diet they have available in your yard.
If the bluebirds successfully raise young in your house, you can expect them back year after year. Be sure to clean the old nest and debris out of the house, I usually do this in the winter. The cold weather seems to kill any lingering bacteria in the house and makes it seem fresher.
I love most all birds, and feed them all year long. But I can honestly say that the bluebird is my favorite. Their beauty alone makes them special, and they have this wonderful warbling song that is almost lyrical in nature. They are no doubt one of our sweetest friends.