Certified GKH Gardening Expert
Normally just prune enough to shape the shrub or to remove the spent blooms. Also remove any dead or damaged limbs to the ground.
If some time has elapsed after flowering and the plant blooms on new wood, look for developing buds and be sure not to go any further.
Here are tips on rejuvenation pruning:
I'm sorry but we need to know the name of the plant. Pruning depends on the type of plant, when it blooms and how it has been pruned in the past. If you can post a picture, we might be able to answer all three points.