The mistake nearly everyone makes is planting too deep. Find the root flare, where the trunk widens out at the base, and make sure it sits at ground level or a touch above once you're done. Nursery pots often have soil piled over it, so scrape down until you find it.
Dig the hole two to three times as wide as the root ball but no deeper. Tease out any roots circling the pot, then backfill with the soil you dug out. Don't fill the hole with compost, the roots tend to stay in the soft stuff instead of spreading.
Water it in well, put a ring of mulch around it a few inches deep but keep it off the trunk, and water deeply once a week through its first summer. Only stake it if it's in a really windy spot, and take the stake off after a year.
