Thanks for writing. The best time to prune weigela is in midsummer, after the big flush of flowers fades. How to prune depends on why you're pruning ---if the plant is too large you can selectively cut the stems back to an appropriate size. If there are certain stems that are in the way, you can remove part of them or remove them entirely. If the plant looks good and fits its space, you may not need to prune it at all.
---Justin, Senior Garden Editor, BHG.com