Exercise 1: Try to draw some of these twigs with various leaves.
Exercise 2: Draw a real leaf of a plant, shrub or tree. I chose a leaf from the ivy (Hedera) that grows almost everywhere. I did not start with the outline but very lightly with the five leaf veins that point from the branch to the furthest ends, like the hands of a clock. With some shadow and/or color it is nice to make the leaf a little more lively.
THE ART OF SIMPLIFICATION:
It is neither feasible nor necessary to draw all the leaves in a tree as if each leaf were on the table in front of you. There are also far too many in a tree. Of course you want at least to give the suggestion of leaves in your tree. Simplification is then the trick. Comic artists can do that very well. Here’s a cartoonish example of a small group of leaves overlapping each other.
Exercise 2: Draw such a group of leaves in the cartoon style. You can also make the leaves more pointed if you like.
Exercise 3: Draw a tree with a foliage consisting of leaves in groups. It doesn’t really matter where you start. Let the groups point in various directions. Alternate slightly between pressing harder and softer with your pencil.
Exercise 4: With the following trees, especially the leaf-like outline is crucial. Within that outline you won’t have to draw many leaves. Draw these three different kinds of trees.