There are endless methods and opinions regarding pruning. The method and philosophy that will work for you depends on the context of your specific situation — is the tree already full grown? Are you considering growing the trees from seed, from rootstock, etc? The following resources will expose you to some of the methods.
• Pruning – Jeffrey Johnson, MN Landscape Arboretum arborist
• Pruning – City Fruit, non-profit of Minneapolis, MN
• Pruning – Hilary Rinaldi, professional landscaper
• Pruning – radical take on “no-prune” method. also this link
• Mature Fruit Tree Pruning Technique — Midwest Fruit Explorer member Allen Cosnow explains theory/practice as he prunes an overgrown apple tree
Other Interesting Stuff
• What is Backyard Orchard Culture – Includes ideas for high density planting, successive ripening and pruning in a backyard orchard.