Wait to prune young blueberry bushes until their fourth year. Then during the early spring dormant season remove dead, weak, or short terminal stems, as well as any crossing branches that block light from the interior.
Blueberries form flower buds on strong one-year-old wood; plants that don’t have vigorous new wood should be pruned to encourage new growth. On mature plants it may be necessary to thin older branches that have the most fine twiggy growth and the fewest strong one-year-old shoots. Cut them at the crown to encourage new growth. Head small branches with small flower buds.
Judge the amount of thinning needed by the size of the berries. If they have been small, prune more heavily the following dormant season. If large, limit pruning.