A simple study you may like to try is to draw, in outline, lightly with a soft lead pencil, the corner of the room or a few assorted objects that are on the table or sideboard.
Then fill in with washes of the appropriate color. Let each wash dry thoroughly before you attempt the next otherwise they will merge with each other. When you have completed laying in all the washes, let them dry off and on top of them delicately put in all the surface detail, textures and modeling. Aim for good shapes and good tones.
The object of this study is to give you confidence with your washes and to make you cover the whole area of your picture.
A second study aims to help you to leave out painting and leave in the white paper. Set out a white jug or object on a colored towel or mat and have plenty of newspaper underneath the towel. Here you have practically a white to grey picture, enlivened only by the co lor that the jug or white object is standing on.
This will be a good study in leaving white paper for the highest lights and because of the greys of the newspaper and the modeling of the jug, a good exercise in monochrome wash. Make sure, too, that the background is one that enlivens the tones of the objects, either a very dark or a brightly colored one will do. If the background is too near in tone to the white jug it will be very difficult indeed to render the nearness of the tones with watercolor wash. Better leave that to the opaque media. Proceed more or less as you did with the first study.
As a variation, why not try drawing a few random objects, first with conte or carbon, and model them up in the usual way but leaving plenty of white areas to take some washes.
In short, don’t overdo the tone otherwise there will be no room for any color. Then, when you are satisfied with your drawing, flood some washes over it. You may find that because of the density of the black lines, the color you use will have to be quite strong in hue.
You will also find that it is possible to overpaint with opaque color on top of a strong drawing, either leaving the lines of the drawing showing or else covering them up completely. These possibilities give you great latitude and help you to go on when all seems lost.