Summarize this article:

The ideal height for this shrub is between 6 and 10 feet, because this height allows it to be full, lush, and compact.  Always use sharp hand pruners when pruning this shrub. Even if it is grown as a hedge, hedge shears should not be used. They tend to shred the leaves. Find a growth bud on the stem that is located at a height of 6 feet (1.8 m) or less. If it has not reached its mature height yet, the stem can be cut down to about two-thirds its current height. Make the cut at an angle just above the growth bud. While Tardiva is a young shrub, it does not need to be cut back drastically to reduce its height.  A light pruning is all that is necessary. It will keep the shrub more compact and encourage additional new stem growth which means more beautiful hydrangea flowers. Make the cuts at an angle above a growth bud with sharp pruners, but find a growth bud that is not very far down on the stem. Older Tardiva hydrangeas sometimes need serious pruning to help them look their best.  This type of pruning is called rejuvenation pruning because it does, in a sense, rejuvenate an old bush. Cut one-third of the oldest stems right off at the base in winter or early spring each year for three consecutive years. The height of the remaining stems can be reduced by one-third each year as well to help reduce the overall size of the shrub. In the fourth year, most of the stems will be new and the shrub will be full-looking. Dead branches should be removed completely and immediately, as soon as the dead branch is noticed.  This can be done at any time of year. When doing your annual pruning in the winter or early spring, cut out any branches that are growing at odd angles and crossing other branches. These branches can rub against other branches, causing wounds that open the shrub up to disease and boring insects.

Summary:
Maintain a height of 6 to 10 feet (1.8 to 3.0 m) to achieve ideal growth. Refrain from excessively pruning young shrubs to maintain a compact shrub. Prune older hydrangeas to rejuvenate them. Remove dead or odd-growing branches to tidy up your shrub.