Choose a dry, finished monotype. Monotypes with wet ink will smear when the oil pastel is added. Oil pastel also will not adhere easily to damp paper.
Consider where you will add the oil pastel. Monotypes are generally known for being black and white, and adding too much color may detract from the quality of the original piece of art.
Apply the oil pastels. Oil pastel artist Sarah Theophilus recommends laying down a thin layer of color first, then blending and building layers slowly for more control over the finished look.
Apply an oil pastel fixative. The experts at How to Draw and Paint recommend spraying an oil pastel fixative over the whole monotype when the piece is completed, as oil pastels never fully dry out and can be smudged or damaged without a fixative.