winter pruning typically stimulates growth, while summer pruning slows growth and can stimulate fruiting.
some plants fruit on new wood, some fruit on one year old wood, and some fruit on older wood. that's going to have a major influence on when and how to prune each plant.
there are many plants that will do just fine without pruning. make sure you actually have to prune, as it's a lot of work. if your existing fruit trees were pruned previously, you're probably going to have to continue. if they weren't you might not have to. if the new trees you buy are small, then you might be able to avoid pruning even if they're grafted, though seedlings will do better.
I would be willing to bet there's a backyard fruit grower's group in your area. joining is a good way to get some information about pruning, though it will likely be oriented more toward intensive pruning as opposed to the folks around here who seem generally to avoid pruning if possible.