It´s ok. Just take more care about the material and how to express it. For example the jeans material. I wouldn´t give it such a white highlight.
And think about the light direction. You can use even the simpliest coloring (cell shading) and get good results if you keep your rules straight till the end (light direction).

You can improve the 3D looking of colored images by using reflex light. Time to mention here my poor english: You are reading poor english! I mean most images are colored to look more plastic/3Dimensional. To do so check out were light is reflected. On your image white light is reflected by the white floor. So you have to draw some white light at the edges in the shadows. And more important!: Objects cast reflected light back to themself. For example if light comes from top breast for example are shaded at the bottom side. But the skin reflexes the spread light and from the lower side a little shine comes from down and left and right (usually from the arms). That means the darkest shade is not on bottom but somewhere on the lower side between bottom and top... A simple effect to rise the quality veeeery much.