What you’ll need:
First, as with almost any drawing, you will need to lightly outline the general shape of your clouds. Don’t focus on perfection here. Allowing yourself to draw freely will lead to a more organic look and more realistic results in the end.
Next it’s time to block in the area surrounding your clouds. Because clouds are white, it is easier to start by filling in the background first to give you a sense of the cloud’s form. Try your best to smoothly shade the background by blending with a piece of tissue, a blending stump, or your finger if necessary.
Once you have your background in place, and the negative space that will become your cloud, you can now begin giving it volume by shading. Start lightly to get a feel for how dark you will need to shade to achieve the lighting conditions you’re looking for. Even though a cloud is white, it still has highlights and shadows. Generally, the edges of clouds are stark white, with the interior being a very light shade of grey. However, darker grays on top of whiter whites will give you the appearance that the sun is coming from directly behind your clouds.
Remember, always start out light. It’s easier to go back over your shading to get it a little darker than it is to erase and go lighter!