Pruning & training trees, shrubs, perennials, and fruits can be intimidating for gardeners.  Major pruning of large shade trees, including nut trees such as pecans, should be done by a professional arborist.  Most other pruning, and all training, can be done by homeowners.  The attached file is a pruning primer.  More information on pruning fruits can be found in the Edible Gardening Classroom.