When you prune flowering shrubs really depends on when they flower. Spring flowering shrubs like forsythia, lilacs, and flowering almond form flower buds on the previous year's growth, and should be pruned after flowering. Pruning them in early spring would remove the flower buds and result in very little flowering.
Plants that flower after the end of June, like goldflame spirea and potentilla, form flower buds on the current year's growth, and should be pruned back by one third in early spring and again lightly after they have flowered.
