After harvesting fruit, remove all canes that bore fruit – these will die soon anyway. During the dormant season (winter), prune away weak, broken and damaged canes. If you have rows of plants, narrow each row to about 15 inches wide and thin to 4 or 5 strong canes per foot of row. In April shorten the canes when the first new growth occurs to encourage new canes and increase yield.
If you want to have a single harvest, cut all canes to ground level in early spring during the dormant season. Remove suckers from new growth to keep row width manageable. If you wish to have an early summer crop, allow canes to overwinter. In the winter, remove weak, damaged canes and the tops of canes that fruited the previous fall. Thin to about 4 to 5 strong canes per foot of row.
Read more about pruning raspberries.