There are so many techniques for creating with oil pastels - it would be near impossible, and unnecessary, to learn all of them before beginning. Rather, it is wise to know some basic techniques and then learn through practice, study, and experimentation.
So, let's get started.
Suggested tools for oil pastel work include your surface (I suggest beginning with paper for watercolors), an oil pastel set (student sets are a good start), and a few blending/scraping tools such as blending sticks and a palette knife. Always begin your pastel work with a pencil sketch. This will help you plan your techniques, which is an important key to success in oil pastels.
Once you have your sketch, you can begin applying the oil pastels. Use layers of oil pastel to give you more control over the intensity and texture of your pastel colors. This technique adds depth as well.
Another technique for applying oil pastels is to use strokes that match the finished look you want. For example, use short linear strokes for short grass or rough surfaces. On the other hand, long natural strokes work well for a flowing look (like long hair or a smooth fabric).
Shadowing with pastels for dimension can be done with techniques like short hatch marks, or just smooth, blended shading. Either way, first choose shades of pastels similar to the base color and begin at the edge of the object, opposite where the light source should be. You can much more easily work in increasingly darker tones than to lighten an area once it is too dark.
Another important oil pastel technique is scraping. For drastic color changes to an area, use a sharp edge to simply scrape off as much as possible of the existing color, and apply the desired oil pastel. This helps keep colors from getting “muddy” by mixing with previous layers. To replace a dark color with a lighter one, try scraping as much as possible of the dark pastel off, and covering with a thin layer of white pastel before applying the color of choice. Another effect/technique in oil pastels using scraping is graffito*, in which a sharp line is scraped in the existing pastel color, creating a light-colored line (such as the veins in a leaf). Scraping can also be used in areas of intense color to soften or give a “fuzzy” effect.
There are many other techniques for oil pastels such as thinning/softening the pastels with turpentine (apply either from the softened pastel stick, or with a brush) for various effects, and more. Remember that success with learning oil pastel techniques comes with practice and experience, so don’t be afraid to try different techniques, surfaces, and tools. If you'd really like to take your new talents to the next level, consider enrolling in an online art class or two. And most of all- have fun!