Create a light sketch of your drawing on watercolor paper using a drawing pencil.
Fill in your drawing with color using oil pastels. Add color with oil pastel crayons in the same manner as you would with a pencil or crayons, by sketching the color onto the paper. Oil pastels smear very easily, so right-handed people should start coloring in the left areas of the canvas and left-handed should begin on the right. Work on coloring small sections at a time.
Fill in a base color. Oil pastel colors are very saturated, so start with a color that is one to two shades lighter than the middle hue as a base color. Fill in the area with a color, and smooth the color using a cotton swab.
Add dark shading using dark-colored pastels. Fill in dark areas, overlapping the edges with lighter areas. Blend the colors using a cotton swab. Layer the colors, blend, and layer more until you create desired shadows.
Add light shading using light-colored pastels. Sketch light colors onto highlighted areas by layering the colors and blending. Use white pastels to fill the most highlighted areas.
Add details to the final piece. It is difficult to obtain sharp details with oil pastels. To create details, draw long strokes onto the paper, then go back over the strokes with a cotton swab to smooth the line and clean up the edges. Pull excess cotton off the swab for a firmer tip to work with.
Fill the background with color. Oil pastels are thick and messy, so keep this in mind when filling in a background. Fill the background entirely with color, in small areas only, or choose a different medium such as pencil, chalk pastel or oil paint to create a varying texture for the background. Alternatively, thin the oil pastels with turpentine and brush the thinned oils on the background for a more translucent effect.
Apply spray varnish over the finished piece to seal it. Apply thin coats of varnish, following the can instructions.