How do you make sure the "right" animal is using your bird nest?

Learn all you can about the birds you want to attract and offer them a box that opens at the top and the front or side. Monitor the nest box, and evict starlings and house sparrows.

The safest solution to insect infestations is physical removal and soaping the inside top of the box. If insects infest the box during nesting, apply a light dusting of rotenone or pyrethrin. Do not use chemical sprays.

If snakes and climbing mammals are a problem, use physical barriers to deter them. Try a PVC pipe over your metal bird house pole, or metal sheeting on a tree or wood pole. Smear the PVC or metal with Vaseline laced with hot (cayenne) pepper. Avoid automotive grease, it can be lethal to wildlife.

Put a predator guard over the nest entrance hole.

Do not use bird houses with perches below the entrance hole.

If you find birds attacking the adults, eggs or nestlings, what you can do depends on the perpetrators. Eliminate house sparrows and starlings. 

All other birds are protected by federal and state laws. You may not harass or otherwise harm hawks, owls, falcons, crows, grackles, jays and shrikes