A common mistake with tree projects is planting a tree too deeply. Click here for an article describing what can happen when not enough attention is devoted to proper tree planting technique. This article was posted on the blog Topics in Subtropics, by Ben Farber who works for the University of California Cooperative Extension and is the soils/water/subtropical crops advisor for Ventura and Santa Barbara Counties.
Click here for more advice from Solano County Master Gardeners on proper tree planting technique. The BTF website has additional information on tree selection and pruning at this link.