First, make sure you work out the figure properly before starting on the clothing, the right leg looks disconnected from the body and its too long. Also make sure you add gesture to the hair because it looks stiff. Then, add the clothing and wrinkles to wrap around the shapes to make them look dimensional, and to show perspective. I did a quick sketch to show you what I mean, and to show you how to simplify the clothing so that it reads more clearly :)