One of my first ever bluebird boxes I erected has successfully hatched 4 Eastern Bluebirds.  This box was setup outside of the office where I worked and the adults took to it right away.  This was odd because I also had many other boxes setup out in the natural areas of the propety.   The tree swallows nested in most of the other boxes.

Once this brood had fledged, the adults raised another, plus 2 other pairs of bluebirds took up residence in some of the other boxes on the property.

I had pounded in a metal fence post and attached a bluebird box to the top of it.  I had my box facing south, there is some  debate as to the direction, but south worked for me.  The key to success is the opening of the box-1 1/2 inches in diameter.  Also, be sure to remove house sparrow nests if they begin to build a nest.