To paint a landscape, it is a good idea to use a purple pastel pencil because this color blends well into those of the landscape without darkening or staining light colors as much as black. Both charcoal and violet pastel are easily erased with absorbent paper or a damp cloth so do not worry, you can correct your drawing! Make your drawing and if you make a mistake, erase it and try again.
Wipe your brushes and knife to clean them. Wash the brush you used for the color study (if you used one) with the thinner: simply dip the brush into the thinner and wipe it with your cloth.
Or if there is not much or no white in the primary color brown blend obtained during the color study, you can use it for your thin layer of brown. Dilute the paint by dipping your brush in turpentine or odorless thinner (those of the brand Winsor and Newton are of good quality). Then dip the brush in a little paint and mix until you get a clear, very liquid and translucent paint. Fill in the light areas of your painting based on your preparatory study. Use a little more paint to fill the medium and darker areas with the burnt sienna while continuing to dilute it until it has an ink texture. Even dark area paint should contain a good amount of thinner. The more diluent you use, the more this translucent layer of burnt sienna will dry quickly.