Join Date: May 2020
Location: Southeastern US
If you are starting with emersed growth, you are going to want to wait for some heathy new growth that is adapted to underwater conditions, then cut and replant the healthy tops and ditch the older growth that is probably looking ratty anyway. Beyond that, I think you should experiment and get to know how your plants grow. Each species has its own vibe and takes to pruning differently. If you have healthy growth you can recover pretty easily from decisions that don't pan out.
Trimming is not just cosmetic though. It's critical to cut out unhealthy growth, and to make sure light and water flow reaches all parts of the tank.