Make copies first, to practice on ... it won't come easy, if you have not learned how to do this yet.
Use colored pencils and try shading it ... to show the contures of the body and fabric. Pencils are probably the best tools to work with at first because they are forgiving.
First, stand in front of a mirror and shine a bright light like a flash light or desk lamp on yourself in the mirror to study how light and shadow work. You will see that the fabric closest to the light will be a lighter color than the fabric on the dark side. And your skin and hair too. Notice how folds in the fabric look when hit by a light on the side. Notice how the shadow follows the shape of the body undeneath the clothing. Notice where the dark shadows are ... and notice the hightlights. See how it looks under different conditions and moving the light around. If the light is really bright there should be a big difference between the shadows and the hightligts. If the light is softer, the diffenence with be less and the change of shadow to light will be soft and more gradual.
Now, on your drawing, imagine a light source ...for example imagine that a light is coming from the upper left. Next, create shadows on the far side of the light and in the folds of the fabric (by darkening the color, or even adding some gry to it). Make the color lighter and brighter on the side the light is on. And, as they tell makeup artists when they are conturing faces .... blend, blend, blend.
If this is too difficult, then practice using simple geometic shapes that have curved sides like people do ... a ball, a cone, a tube, etc.
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