The farther the birds' house is from trees, the better. Make sure there are no trees taller than the martin housing within 40 to 60 feet. Install the house at a height of 15 to 20 feet. Stay away from tall bushes, shrubs and vines. And don't attach wires to the house.
Timing is tricky.
It's only the young martins, who arrive later, who are looking for a new place to call home. So if your new house is up too early, it's likely that more aggressive birds will move in before the young martins arrive. To entice young martins to set up housekeeping on your course, open your house about four weeks after the first martins are scheduled to return to your area. Then, no matter what state you live in, keep your housing open through June when some martins are still arriving to begin nesting. To keep competitive birds at bay, keep the martin house plugged up during the off-season.