Many people, when deadheading roses, just snap the old flower heads off. But if you want to continue the display into fall, you have to prune back to a bud in a leaf axil lower down the stem to encourage strong new shoots. Prune to an outward-facing leaf to keep the center of the rose bush open.
Wild roses should not be deadheaded because they produce attractive hips in the fall. After deadheading, fertilize roses to boost growth and encourage more flowers later in the summer. Use a rose fertilizer or one high in potash to encourage strong shoots. Avoid a high nitrogen fertilizer as that will result in soft, sappy growth that is more prone to attack from pests and diseases. If you are going to spray your roses with a chemical to protect against Japanese Beetles I recommend that you do it late in the evening. Some products are toxic to bees and by late evening the bees are back in the hive. I discourage powder form as it leaves a residual on the leaves that the bees can still pick up.