Well, I would prune it only if it is reaching out and grabbing people, or if it is seriously unbalanced. If you do need to prune, here are the rules of thumb:

It is best to prune right after bloom, since the flower buds develop in the fall.

Don't remove more than 1/4 of the foliage in any one year.

If a branch is pruned back to bare wood, it stands a 50% chance of dying. If a large branch must be cut, prune back to a side branch.

When cutting leafy twigs, cut just above where one year's growth ended, and the next year's began. That will encourage two or more sprouts to develop, making the plant bushier.

After a heavy pruning, watch the watering: the plant will be using less water.

Hope this helps!