Am I clairvoyant, or what?? There are a couple of things you need to know about this shrub. Most (if not all) of 'em bloom on new wood, so if you prune 'em at the wrong time OR too hard, they will not bloom. Their inbred desire is to become a really big 'fountain' shape (fairly narrow at the base and quite wide at the top). They also have a tendency to shoot up REALLY long stems that won't bloom for at least 2 seasons.
Depending on what your clients want, and the amount of space they have, they can be trained as a hedge or as single specimen shrubs. You said 8-10 years old - I'd guess they're pretty big. Try not to prune more than 25% away in any 1 season. If you prune more, it's not likely to kill it, but it will take a long time for it to recover completely.
I'd start by taking out (at 6" above the ground) the long, whippy stuff. This will make the pieces below the cuts bifurcate and fill in at the base. Then if there are pieces trailing on the ground, take those out (your choice of where to cut). They can and will tip root with soil contact. Unless they want a hedge, then let 'em be.
Be sure and walk around the shrubs as you work to keep the look evened out. Try not to use hedge trimmers (gas or electric) on 'em, it's a very contrived look (again, unless they WANT a hedge).
Good luck.