Full sun if possible - prune immediately after flowering, taking off the spent flowers at the bottom, with a bit of stem as well.

I have grown one of these for several years now. I don't give it much in the way of pruning but if it is spreading too far, I cut out the offending shoot completely

After bloom, there will be a section of leafless stem, often with seed pods attached, where the flowers were. Just below this, there will be a whorl of crowded leaves and buds where last year's growth ended. The best place to prune is just above one of these whorls. If you need to prune farther back, look for hints of the whorls in the bark texture, and cut in the same place, or cut just above a side branch, especially when cutting larger branches.

Thank You for your advise