Wash off a little of potting material around the root ball so the roots make contact with your soil. You might need to use a knife to make cuts through the base of the ball to stimulate root growth if it's really potbound.
Clear a three foot area around the planting hole to allow for watering and to prevent any competition from grass/weeds with your tree.
Dig the planting hole the same height as the root ball. This is important. You don't want to plant a citrus too deep or you'll get root rot.
Fill about halfway up the root ball then add water. Then fill the hole with soil and tap it down lightly. Add about another inch of soil on top of that.
You'll want to build a six inches high watering ring, and make sure when you water it the root ball doesn't become exposed. If so you'll need to add more soil.