This looks like a great spot for a bluebird box! Both the tree in the center of the photo and the white tree in the background appear to be good candidates. If they're at least 100 yards apart, you could even add a box to each of them (they need to be that far apart to avoid territory overlap). As far as specific conditions on where and how to hang the bluebird box, I'll refer you to the MyWoodlot Activity Install a Bluebird Box. Check out in particular the how-to information labeled "Bluebird Nesting Box Information" for installation tips.