The Autumn season is as good as any to plant new trees and shrubs, provided some late season care is given to these plants.
It appears as though using the mobile app has rotated my pictures, so please bear with me during my first Instructable.

Step 1: Decide on the Project

Our project here, ultimately, is to construct a windbreak for our home in the country; this is one integral piece of that life project.
We've chosen for this portion to be a hedgerow. After perusing the slim-pickins still unpurchased at the store, we chose Hedge Cotoneaster in one gallon pots and got a screaming deal of 75% off the original price. We bought the last 7 plants. Provided the plants thrive once Spring arrives, cuttings can be made and the hedgerow can be extended to completion; or so is the expectation.

Step 2: Existing Landscape

Here we have the entire North portion of our property. When we bought this home last year, this was still a field; we've been busy, but it is not yet complete in our eyes. We already have begun with the Norway Spruce and Austrees shown in the pictures, but did suffer about 70% Austree loss due to unknown reasons--my thinking is that since I didn't coat the tops of the cuttings, they rotted from the top down.

Step 3: Location, Location, Location

Since the end goal is to create a windbreak, we continue to target a location in the Northwest corner where the winter winds prevail. The spot was chosen and preparation work begins.

Step 4: Prep Work

After deciding the starting point, I strung a wire line so the hedgerow can be kept straight when planting. It is real easy to get the line crooked without this step. This is a simple step and proves to be quite effective. Note that the line was wound around the stakes about 4"above the ground. I've found in a couple past experiences that holding it flush on the ground actually can create a crooked line as it can get moved around and held out of position by grass and/or dirt.

Step 5: Gettin the Dig On

Now that all the planning has been completed, it is time to make some tempered steel happy. With these one gallon sized plants, experience from the scores of previous plantings tells me that two shovel widths, square, is large enough for the root ball. Most directions given to consumers on the packaging states to make the hole 2-3 times larger than the root ball's diameter. I don't like to dig round holes, so square it is. Begin digging your plant home; keep the removed soil available, you'll need it later.
Determine the depth that will be required; this is actually pre-determined by the root ball itself in that the top of the root ball needs to be flush with the ground. The base of the plant should always be at that level. Making the plant too tall in the ground will create issues with run-off, the plant will be stressed and not grow correctly. Planting too low will also stress the base of the plant's trunk/stem and can actually cause rot. It is important to note that making the hole a bit deeper, before setting the plant into the hole, can actually aid in plant growth as long as the plant is spaced upwards with loose dirt underneath the root ball and the desired height is still met.
At this point, I usually square up the sides of the hole vertically. My belief is that this forces water to more effectively flow into the plant's new home, versus having to penetrate already-compacted, old soil.

Step 6: Finding the New Home

After the dimensions of the hole have been both determined and met, it's time to put the plant actually into the ground.
Gently wriggle the plant from the container. Sometimes this requires a slight tapping of the sides of the plastic pot, sometimes they just slide right out. Each plant is a bit different so take care not to create undo stress in this step. Find the happy place for the plant within the hole and set it in. If you're trying to keep even spacing, as in this effort, measure [however makes you happy], and set it in the hole. If this is the case, and you've not created cookie cutter holes, the plants will likely be a bit off-center. This is OK, so do not worry about it. If spacing does not matter you can simply make the plant become the finite nucleus of the hole if you so choose. Know that there is enough room for the roots to be happy; of course, if the hole is large enough. Perfection is not required, but you need to be happy with the actual location as this is where the plant will grow.
Note how compact the root ball is. You need to undo this a bit by kneading the root ball to loosen it up. This 'tells' the roots that they are no longer bound by a plastic pot and can spread as much as they are genetically allowed. The root ball should end up looking kind of the same, just looser.

Step 7: Fill 'er Up

Time to fill the hole and make the plant's location permanent. Sometimes i get 'particular' and remove all of the attached sod with purpose of replanting it somewhere else, sometimes it is not as complete. For the most part, I am more concerned about completely removing just the more nasty weeds like dandelions, bull thistle, wild parsnip, canadian thistle, etc., the ones that can cause problems later.
Shovel in the dirt you've set aside and get it about full to the ground level. At this point, I usually vertically tamp the outer perimeter of dirt, kind of like vibrating cement within its molded form. It loosely packs the perimeter dirt in, while still keeping most of the fill loose enough to allow good root growth. When this is complete, overfill the remainder of the hole. This will provide enough dirt to allow for natural soil compaction and to make sure there is enough fill to keep the plant happy for years to come.

Step 8: Finishing Steps

Using most of the dirt removed in making the hole, fill the remainder of the hole with dirt; creating a mounded feature above the hole. This will allow for a natural compaction over time, yet still provide enough soil to maintain good plant health. Don't be shy here and make sure the fill is about 20ish% above the ground level, when compared to the depth of the hole.
When an adequate amount of fill is achieved, it is now that some hand work needs to occur. Carefully uncover any branches/stems that were inadvertently covered and wipe dirt away from the central base of the plant. It is important here that the full mound is adequate enough to begin natural compaction, as well as keeping the plant in place. This basically means that the mound should be (about 50/50) on the root ball as well as the hole perimeter.
Water the new plant, copiously. In this plant size, we used about 15 gallons to completely saturate the new dirt. Note there will be initial compaction/settling that occurs. This is both OK, and expected to be normal.
As the Autumn leaves fall to the ground, they will be placed onto the root balls for mulch. After Winter, weed barrier will be staked to the ground so these can grow, unchallenged by weeds and grass.
Stand back and admire your work, you've earned it. Crack a beer (or three), and celebrate helping the Earth and humanity while improving your property.