Hi Becky
I haven't had much luck with my bird houses. I can't give you expert advice, that's for sure.
I changed locations of my houses last year. One mistake I made was having the Wren house with a copper roof in the sun. I wasn't thinking about the heat in there. I also had a couple to close to the feeding area.
What type of bird is the house for? As far as how close it is it would depend on the bird. Some birds will have no problem nesting nearby a house. My friend, who isn't even into birds, had Chickadees only about 10 feet from her back door in a decorative house. Another year she had Blue Jays in a tree near her back door. I have houses and haven't been that lucky yet ;)
I brought metal openings (I forget what the name is for them) to cover my houses entrance holes to make it sized for Titmice and Chickadees. We have House Sparrows around sometimes. One year we had Wrens in a house and the House Sparrows took over and broke all the Wrens eggs. I'm hoping this year for Wrens, Chickadees or Titmice. I would be thrilled.
I checked a book out of the library awhile back that had a lot of info about bird houses and choosing and placing them in such a way that the birds would actually use them. I didn't pay it much mind at the time because it was back in the early fall so I wasn't really thinking about bird houses. Maybe I'll go check it out again.