How should I landscape my yard to make my home more efficient?
To make sure you get light in the winter, you need a deciduous tree (one that loses its leaves in the winter) planted on the southern side of your home (where the sun's rays are the strongest for people in the northern hemisphere). Pay special attention to the size the tree with grow to when mature, both in height and in width of the canopy. I'd recommend playing it well outside of the canopy's reach from your home to protect not only your siding, but also your foundation from roots that will travel often twice the range of the canopy.

Take special care to check for buried utility lines and place your tree away from any of them. You also want to be sure it is not too close to a sewer line, since the roots have a habit of growing into and clogging sewer pipes.

Finally, realize that a tree will add beauty and natural energy efficiency, but it will also add to the maintenance of your home, particularly from leaves clogging the gutters, and falling branches. If your only goal is energy efficiency, you may be better off upgrading to energy efficient windows and sealing any drafts.