Reasons for pruning are to remove diseased, dead or broken branches, to maintain a size and shape within your landscape design, and to maintain the natural appearance of the flowering bush. There are two methods for pruning shrubs--heading and thinning. The most important factor in pruning flowering bushes is timing, and the correct time depends upon whether the plant produces blossoms on old wood or new growth. Bushes that produce their blooms on old wood (previous season's growth) should be pruned after they are finished blooming, and bushes that produce their blooms on new wood/growth need to be pruned in winter or early spring, when they are dormant.
Remove any diseased, dead or broken branches immediately, to ensure the health and integrity of the flowering shrub. (You do not have to be concerned with the plant being dormant or if it has finished blooming.) Where you make your cut will depend upon the location of the branch that needs to be pruned. Diseased branches should be removed completely (down to the base or trunk of the shrub). Broken and dead branches can be pruned either at the base of the shrub or where the break/dead wood is located. If you are not cutting off the entire branch, prune approximately ¼ inch before a bud.
Use the "heading" pruning technique to contain the shrub within your landscape design, and to shape it by cutting back branches. Prune the branch back to a healthy bud, and make your cut ¼ inch in front of the bud. This should be done according to the type of flowering bush that you have (blossoming on old wood -- or blossoming on new wood), which would be either after the shrub has finished flowering or when the shrub is in its dormant stage (winter or early spring).
Use the "thinning" pruning technique also to contain the shrub within your landscape design and to shape it by cutting out select branches down to ground level (multiple stems) or in some cases (when you have a single trunk) back to the trunk or main branch. Thinning allows more sunlight into the flowering bush, and it also increases air circulation. Follow the same timing rule for thinning as you do for heading. More than likely you will use a combination of heading and thinning when shaping and maintaining your flowering bush.