I tell you what I do and you can tell me what to do different, or if I'm doing it right.
First I'll make sure the planting hole is as deep as the existing rootball on the tree, to plant at the same depth. But, the hole itself will be about 2.5-3 times the width of the rootball to allow for easier root devlopment in the early stages of the trees life. Before covering the tree with soil I will gently cut a little or actaully tear the root ball out a little to also allow roots to take hold faster. I will also fill a partial amount of the soil with actual miracle grow potting soil with nutrients and fertilizers in it to feed the tree, last but not least give it tons of water to help with the stress of being newly transplanted, and maybe a stake or two for extra support, or to support straight, vertical growth...close??? This is just based off my prior knowledge of planting things, lol.