First of all buy from a reputable nursery. Buy locally. Not only will you have some recourse if the tree dies within its first year, but also the tree will be adapted to your particular climate.
Second, think about how big the tree will be when it is mature. Lay out the measurements on the ground before you dig the hole. Many a healthy tree has been cut down after 1-2 years because it was too close to a building, driveway or other structure.
Third, consider the root system. The roots of any tree will spread far wider than the leaf canopy. Ask yourself whether the roots could eventually cause problems to other plants or to your infrastructure - such as water, sewer lines or septic tanks and drain fields. Willows and poplars are notorious for root systems which seek out water. The shallow root systems of maples are infamous because they hog the water in their area. It is difficult to grow any small plants including lawn grass, under a maple.
If you choose to purchase bare root trees, buy your trees early this spring before they begin to leaf out. Bare root, dormant trees will grow much faster than ones in a container. Don't worry about size. Small trees will catch up with big ones bought at the same time within a couple of years.
As soon as you get your bare root trees home, put their roots in a bucket of water. Leave them to soak until you plant them. Try to get them in the ground the same day they were purchased. Dig the holes only as deep as the root ball but much wider. A hole approximately three times the necessary width is the current recommendation. A square hole is supposed to encourage roots to grow outward rather than circling. Look for the root flare. Plant it at ground level or even an inch above the ground, never deeper. If there are any roots starting above the root flair, cut them off. Otherwise, prune off only broken roots or branches. Put in the tree and fill the hole halfway with soil.
Add nothing to stimulate the tree's growth. It needs to be content with the soil in the area where it lives. Giving it pocket of good soil may convince roots not to grow out of that pocket. Firm in the soil, then pour in water to fill in the hole. When the water has drained, fill the rest of the hole with dirt. Repeat the firming and watering.
It's not necessary to stake a tree, but do cover the root area with two or three inches of mulch..