1. Paint canvas black using black paint with a little colour mixed in. It will still look black but won't be as dull as unmixed black.
2. Draw outline if needed.
3. Create tonal underpainting in single colour, e.g. white, to show areas of light and shadow. Tidy up any ragged outlines with black paint.
4. Add colour if wanted for final painting. Tidy up again with black paint if needed.
5. When thoroughly dry, varnish with UV and colour protecting acrylic varnish. I prefer matte varnish for these.