In general, depending on the type of tree, I would say to plant it no closer than 12-15 feet from the house. As far as determining the spot where you will get the most shade, that is simply putting it in line with where the sun will be. Since the 1st day of summer isn't too far away, I think the sun is about as far north as it is going to get. Depending on the type of tree, 6 inches or a foot either way shouldn't make much difference. Plan ahead for when the tree is grown. Most people forget that trees get huge and typically plant them too close.
