Most discussions about pruning hydrangeas are about cutting them back before or after they bloom, or when they are dormant. There is a bit of pruning that can be done now, when they are in flower to help improve their appearance and encourage branching and flower production for the following season.
This pruning is called tip pruning and should be done during the first two weeks of July. Tip pruning applies mainly to the macrophylla (ball shaped flowers) and lace cap (flat flowers) varieties of hydrangeas. Growing tips of these plants that do not produce flowers tend to grow taller than those with flower.
The foliage of the longer non flowering stems should be cut back to just below the height of the stems in flower exposing the surrounding flowers and improving the overall shape of the plant.