The greatest threat to planting a tree is "transplanting shock".  Proper site preparation before and during planting, coupled with good follow-up care will reduce shock.  The following steps should be followed when preparing the site:

1. Dig a $500 hole

Many times people and businesses spend hundreds of dollars on their tree and dig a $25 dollar hole - one that is small and poorly prepared.  Later, these holes become tree coffins.  All trees deserve a $500 dollar hole.  They should be twice as wide and slightly shallower than the root ball or soil in a container-grown tree.  This leaves a firm base of compacted soil for the root ball to rest on which will not settle when watered.  In addition, the backfill used to fill in the hole will be well aerated and allow water and roots to easily penetrate the soil.  If you are able, you could also dig or deeply roto-till an area at least twice the diameter of the root ball and more in areas with heavily compacted soil.

2. Avoid the clay pot syndrome

Roughen up the sides of the hole so that root tips can penetrate the native soil.  Smooth walls are like cement to root tips and very difficult to penetrate.  Use a pick-axe to break up an especially compacted bottom.

3. Locate the root collar

The root collar (or flare) of the tree is usually slightly wider that the trunk before entering the soil.  In B&B and container grown trees, you may need to remove excess soil to find the collar.  With bare-root trees, the hole you dig should be slightly shallower that the root collar.

4. Prepare the hole

Measure the distance from the root collar to the bottom of the root ball with a shovel handle.  Use this length as a guide for adjusting hole depth.  This practice prevents trees from settling lower than originally grown.  Trees planted as little as 2 inches deep can drown or suffer trunk rot.  It is better to plant 1-2 inches above the root collar than to plant it at or below the original growing level.