An illustration study can begin with a simple observed outline. A leaf provides a familiar starting point, but the exercise is about interpretation rather than botanical identification. A pencil sketch is enough to establish the first version.
Draw the subject several times, changing only one decision in each drawing. Make an edge more angular, simplify the central shape or alter the balance between solid colour and blank paper. Keep the variations together so the differences remain visible.
Choose one version and develop a small composition around it. Repetition, overlap and changes in scale can create variety without introducing a completely new subject. Stop occasionally to look at the whole page rather than polishing one isolated detail.
End by noting which change made the biggest difference. This creates a useful record of your visual reasoning. A finished illustration may emerge later, but a page of purposeful variations is already a worthwhile outcome.