Suckers and water sprouts grow rapidly straight up. They don't produce fruit, and shade out the spreading branches that do produce fruit. They can be plucked off when they first appear in June much easier than cutting them off later. Or, they can be tied down so they grow outward and become productive branches. Fruit trees can be pruned in the winter, spring, or summer.
Winter pruning causes a tree to grow more vigorously.
Spring pruning, after the fruit has set, keeps dwarf trees smaller and doesn't reduce the fruit crop as much. Cutting back vigorous apple and pear twigs to three buds in mid summer will encourage more fruit spurs. Fruit will have the most flavor if it is allowed to ripen on the tree and eaten right away. It will store longer if it is picked before it is fully ripe. When ripe, the green background color will change to yellow.