Prune to shape and clean out—dead wood and worn out branches, along with weak and spent canes. Spring is the time to correct problems with overall form, or reduce the height of roses that are outgrowing their space. Most roses bloom on new wood, and tend to have reduced bloom on old canes.
Let the "Rule of Thumb" be your guide: New growth about the diameter of your thumb make the best canes. If the branch is bigger than your ordinary loppers can tackle (1-1/2 inches or larger), it should be removed.
For most rose bushes, leaving 6 to 8 strong, healthy canes is ideal to produce a full, shapely plant, without overcrowding. Floribundas or shrub roses tend to have more branches by nature, so you may want to leave more canes on those types of roses. For most roses, spring pruning should reduce the overall height of the bush to 18 to 24 inches. The shorter you prune, the fewer blooms you will have, but the blooms will be larger. Leaving taller canes will produce smaller blooms in more abundance. Remove all dead, damaged, and diseased canes. Also remove crossing branches, and thin so the bush is open and ready to accommodate new growth.
Spring pruning is dependent on the weather. Keep an eye on your plants and the temperatures; time your pruning just as the new growth starts. You generally don't want to prune if there is still a chance of a hard frost, which would damage the tender new growth.