The "scatter" option on Photoshop brushes is hugely useful. With it, you can add in patterns of leaves which are just random enough but which form branches and masses of foliage. In conventional paint, I do this by using what I call in highly technical language, a brush with a "mushy end." It's a firm bristle brush where you dab paint on by stabbing the loaded tip at your canvas. Photoshop is much less messy. I love painting images of trees and forests. That's the environment in which I grew up. I am still hoping to live in a place in the USA which is warm all year round and has nice green trees. Florida is warm all year round but its trees are weird and I would have to learn some sort of palm frond technique on Photoshop and with my mushy end.
Photoshop sketch from memory, 7" x 10", June 11, 2011.