Fall is not the best time to prune these plants, especially plants that are evergreen (they keep their green leaves through winter). These plants keep their leaves for a important reason and removing them in the fall is not a good thing. They continue to conduct photosynthesis and make food all through the dormant winter period. The best time to prune all plants is in the spring. For plants that bloom only in the spring, prune them right after they are through blooming, but do not prune them after mid-July. Plants that bloom only in the summer (crape myrtles, butterfly bushes, etc.), prune back in early spring (March-April).