when doing scenes like landscapes, try to imagine that there are no objects, only light. Begin with a dark canvas, not black, but maybe very dark brown. Figure out where your light source is, such as a sun behind some mountains. Then figure out how the light falls on things starting from objects closest to the sun first. So that means clouds. But you're not painting clouds, you're painting the light hitting the light hitting the clouds, so that means painting the highlighted edge of the cloud, disregarding the rest. Then the light hits the mountains, and will cast some highlights on them. But if there is a big cloud in the path, then there should be no highlight in that part. Mentally trace the lines of light from the sun to each object, making a note of where the light is blocked and where it passes. When you paint from dark to light (dark background), the shadows are already there, you only need to paint the light.

In the real world, light diffuses and is not like a laser. The way this is done is by painting your objects, such as mountains/houses darker then normal, and then adding in the highlights and play of light. You should never need to paint a shadow. So paint a dark brown house, then add varying levels of highlights based on the angle of the sun.

When painting an actual sun, remember that it's not a round celestial object like the moon. It's more like a single point of light. The color is white-hot, so white at the center of that point, blending into yellows as you move out. This is a sunset as you would never really see it in real life. And this is a more realistic sunset. Notice that the sun is not round, is actually bright white, and the color (yellows, orange/red) is reflected from the haze and clouds.