Choose a location for your plant installation base on the sun and soil requirements of the plant in question. Dig the planting hole approximately twice as wide as the pot -- the wider the better, so the soil is loose and easy to root into -- and just as deep as the pot.
Cut away the lip of the pot with the utility knife, so the pot is the same height as the soil level. You don't want the lip of the pot to be above ground because it will act as a wick pulling moisture away from the roots. You never want the pot to be buried any deeper then the existing soil level and soil should never cover the flare where the trunk meets the roots or you risk suffocating the plant to death.
Lay the plant on its side and cut an "X" into the bottom of the pot so you cut all the way through and slightly into the roots and soil. Cut a vertical slice up the side of the pot, through to the soil, and on all four sides.
Set the entire pot in the planting hole. If your soil is dry, fill the planting hole up with water and then let it drain. Backfill with the native soil so the ground is even with the soil in the pot, the lip of the pot is under the soil and the trunk flare has no extra soil touching it or built up around it.
Water well. All new plantings need to be carefully monitored for water during the first two growing seasons.