When planting shrubs, the latest conventional wisdom advises you dig the hole as deep as the root ball but at least two times wider. This keeps the tree or shrub from sinking as the soil settles while allowing the feeder roots to grow out into the looser and generally more fertile top-soil. Soil amendments (direct to the planting hole) are also discouraged since most tree roots have a natural spreading tendency and need to acclimate to indigenous soils as quickly as possible.
When planting shrubs, definitely avoid digging a perfect ‘bowl.’ This encourages newly growing roots to remain stationary, circling around and around and not venturing out into the soil. And if your soil is hard clay you will need to dig up a larger area than two times larger than the root ball.
Once you added your tree or shrub to the hole, add some soil to support the tree while you check all the way around to make sure it is standing up straight and is facing the direction you desire. The top of the root ball should be at or above the soil level. If the root ball is too low you can possibly add soil to the bottom of the hole with your shovel, moving the root ball from side to side to get soil underneath. If it is too high you will need to remove the tree and dig deeper. Now is the time to fix anything not proper, not after the hole is refilled with soil.
If the root ball has burlap or a wire cage remove at least the top half being careful not to cause the ball to fall apart. Burlap under the ball will rot. Fill the hole in with soil halfway. Make any further adjustments. Water the soil to fill in any air pockets and help settle the soil. Fill in the remainder of the hole.
Mulch the area around the tree with a few inches of mulch. Keep the mulch from touching the trunk. Moist mulch can encourage rot, pests or disease. Water your newly planted tree or shrub if rainfall does not provide adequate moisture up until the ground freezes.