placement of bird feeders; put the houses where you can view them. After years of customer feedback I still give that advice but add that if possible the entrance hole should face east or southeast for the most success.
In Mid-Michigan Eastern Bluebirds like to nest in fields, meadows, orchards, farm fields, large lawns, and golf courses. Their houses should be mounted on our Wild Birds Unlimited APS birdhouse pole or a fence post approximately five feet above the ground. If possible, face the house away from prevailing winds and facing towards a tree or shrub and 100 feet from the house. Trees and shrubs provide a perching area for the bluebirds to hunt bugs and a landing spot for the young bluebirds when they first leave the house. Eastern Bluebird houses should be spaced at least 100 to 150 yards apart.
I did a little investigating and found a report to back up our customers' theory that birds have a preference in the direction of their house. Cornell Lab of Ornithology has collected research by citizen scientists across the U.S. to reveal that the Eastern Bluebirds will nest in a bird house that faces in any direction. In the northern states like Michigan, however, the birds prefer the early morning sun coming in the front of the house as it faces the east.
The studies showed: "Overall, it is clear that nest boxes facing in easterly directions fledged on average more young than boxes facing in other directions. Our data, therefore, suggest there is a benefit to breeding in east-facing nest boxes at northern latitudes, where night temperatures tend to be colder. No benefit, however, could be detected farther south." 
Cornell is still collecting information on nesting. Anyone can monitor nests - it's a rewarding way to spend time outdoors and participate in science. To learn more go to NestWatch a nest-monitoring project developed by the Cornell Lab of Ornithology in collaboration with the Smithsonian Migratory Bird Center, and funded by the National Science Foundation.