Pruning is one of the most essential and intimidating tasks a gardener can do. The best way to learn pruning is to have someone walk you through it step by step for each plant. That may not be possible for every gardener, so finding other resources is important.
While there are many gardening Web sites available on pruning, a well designed and illustrated book is still one of the best references. The Pruning Book, 2nd Edition (Taunton Press, 2010) by Dr. Lee Reich, is a revised version of his 1997 original. It covers not only the basics of good pruning practices, but also includes the proper pruning techniques for hundreds of plants. Some of the common and uncommon plants covered include, lilac, wisteria, tomato, houseplant, bougainvillea, hibiscus, apple, maple, and chrysanthemum. Beside the essential chapters on pruning trees, shrubs, hedges, fruits, nuts, and herbaceous plants, Reich includes chapters on special pruning techniques such as bonsai, pollarding, pleaching, and espalier. With more than 350 photos, illustrations, and detailed descriptions, this book covers almost any plant you've ever thought of pruning.
For more information on The Pruning Book, 2nd Edition, go to: Lee Reich.