Planting a new tree is best done in the dormant season (late fall, or early spring). This allows the tree to focus its production on its root system rather than its canopy. A healthy tree will have strong healthy roots, so keep this in mind while planning to plant a tree this fall.
Transport your new tree with care. The new tree is a living, delicate organism. If you transport it with care the tree will have a better shot at a successful planting. Its root system is already compromised by being removed from its original growing spot. You want to place the tree in its new home so it can grow what roots it lost in the transplant process.
You should locate underground utilities pipes and wires prior to digging. You want to plant your new tree will as little hassle as possible, breaking a water main or pipe will only make more work for yourself.
Break up the soil around were you want the new tree to take root. By doing this you provide a suitable habitat for the roots where they can expand, collect water and take in oxygen.
Dig a wide hole, but not too deep. The top of the root system grows rapidly. If you plant the tree too deep it makes it hard for these roots to obtain oxygen.
Remove all containers, wrappings, and wires surrounding your new tree. You do not want any foreign objects hindering the new root system from taking root.
You should lift the new tree by the ball of the tree near the roots, not by the trunk of the tree to prevent damage.