I thought I'd share some tips I learned making foliage with Blender! I use Blender for both highpoly + lowpoly creation - texturing is done with Substance Designer :)
First off, curve modifiers are suuuper useful to get organic curves and add more depth to highpoly or lowpoly.
On that note: as a general tip you want to make sure to never have leaves disappear completely if viewed from a certain angle. You can for example use the Simple Deform modifier or a Displacement modifier to give them some bends (+ also by rotating them).
It's explained in detail in this video: Modular Plants
Hope this was useful! :)