Pastel drawings are forms of art done with either chalk or oil pastels. Often, this tool and the substance left by the markings are called chalk. This is because of the tools resemblance to that media. Similar to paintings, or colored pencil art, pastel drawings are colored pictures. The difference between pastel drawings and other forms of colored art is that these pictures can be more realistic than colored pencils, and easier and quicker to create than paints.
A great book on the subject is: You Can Draw: From Pencils to Pastels in 15 Easy Lessons
This can be a fairly expensive media to use, but a simple set of 10 colors is really all that is necessary. Pastel drawings mix colors easier than most other medias, and with a 10 color set, you can create all the colors of life.
Color percentages will vary based on race and the exact shade of the skin (males often having darker skin than females, and tans changing the percentages drastically).
If the picture contains too many, or too heavy, strokes, it starts becoming thick and difficult to work with. You can repair this by simply scraping off excess chalk. Using a small, but hard brush (such as a toothbrush or the brush used to clean electric razors) will often be the best tool available to scrap off thick chalk.
When finished with the pastel drawing, you will want to spray it with a final fixative, such as Lascaux Fixative for Pastel, Charcoal, & Graphite This will preserve the image by helping to prevent smearing. One thing you should keep in mind while creating pastel drawings, however, is that once sprayed with the final fixative, the colors darken. Because of this, you want to make sure that you are creating your pastel drawing just a little lighter than you desire the final image to appear.
Fixative does not offer 100% protection. For that, you want to use a page protector or picture frame with the pastel drawing behind glass or laminate.