Improperly stretched canvas could allow movement of the substrate and thereby damage the finished work. Whether you are using Masonite, other wood substrate, or canvas, creating a textured basis upon which to paint is the initial step in impasto. This is done, most often, without regard to specific placement of subjects. Produce this texture with the tool of your choice, creating a crosshatch of brush strokes of uneven, related sections. Your subject is then painted over this textural base.
Underpaint application can be a way to relax otherwise constricting or restricting painting habits.
By applying this base paint in a more freeform and loose manner, with no attention to small details, you are able to concentrate on the large blocks or masses of color. It might also lead you into a more stylized expression in the finished work as well. The tools used to apply the paint, or underpaint, can vary greatly. Many artists simply super-charge their paintbrushes and apply paint with the same type of stroke and motion that they use to create their smooth surfaced artworks. Application with brushes can be as simple as rolling a paint-charged brush onto the painting surface to achieve a thick painted line.