A very (very) simplified 4 step tutorial to how I think when I create different types of foliage, this applies to how I think when I make bushes, grass and tree crowns for example. Of course this is just one way of doing it, feel free to ignore everything I suggested.
I would say you can apply this to both digital and traditional painting.
What I find helps a lot is to not focus on the details from the beginning, but laying out the base colours first, figuring out what's dark and what's light. And do a lot of layering.
Hope you can read my handwriting 👀