If the canvas is square, the meaning does not matter. If it is rectangular or oval, decide if you want a portrait-type vertical orientation or a landscape-type horizontal orientation. Make very small sketches simply to outline the light, dark and medium areas on the board. Sketches can range from the size of a large postage stamp to that of a business card. The goal is to see the image as if it were remote or in miniature. Do a lot of sketching until you find the best overall effect without worrying about the details.
It can have many details and precise light effects or be done quickly, just to show where are the different areas of light and shade. It depends in part on the level of detail and realism you want in your painting. For a less precise painting style, you can sketch faster, but it should not be limited to “white, medium gray, and black” shades. You must be able to distinguish at least five shades: “white, light, medium, dark and black”. Some painters prefer not to use white and black but only use the shades “light, medium-light, medium, dark-dark and dark”. It depends on the effect you want to achieve. If you do not like your sketch, keep trying out different versions until you make one that you like.
In the tonal sketch, make sure that the light illuminating the person, the objects or the different elements of the landscape is always in the same direction. Pay attention to the position of the shadows. They must all go in the same direction and must be short if the sun or the lamp are in the high position and more elongated if it is earlier or later in the day and the sun is low (or the lamp is low) ). The light always going in the same direction will give more relief to the objects. Draw the shapes of the shadows carefully and most of your subjects will already have some relief. This will give a good Impressionist or realistic picture.
If you want to make an abstract painting, make a quick pencil sketch and decide where you want special effects like stains or brush strokes with a lot of texture. You can even skip the step of the sketch on paper and go directly to the next step.