The best you can do to improve your drawings of clouds is to study them scientifically. Learn to identify the basic cloud types in life, photos, and artwork. The more you study clouds, the more you will see, appreciate, and understand. Your knowledge and curiosity about clouds will be reflected in your drawings.
We all have a cartoon image of a puffy cloud in our heads. This symmetrically lump cloud is a symbol. Real clouds do not look this way. When you start to draw a cloud it is easy for elements of this cartoon to slip into your drawing and ruin the realistic effects you are trying to create. Fight the temptation to draw this symbol.
Even when you are trying to draw a cloud with a more realistic edge, it is easy for this symbol to creep into our drawing. If it is easy for your fingers to make an arc of one size, your fingers will do it again, and again unless you are on the lookout for this pitfall. Note the presence of symmetrical bumps on this cloud. Can you see the influence of the cloud symbol in this drawing?
The trick to a more natural shape is to be consistently inconsistent. Make your cloud shapes and bumps irregular. If you make a bump of one size here, make a bump of a different size there. This will give the cloud shape a more natural contour.
The best way to learn how to draw cloud shapes is to study the real thing. Instead of sitting indoors making up clouds, go outside and see what real clouds are doing. Start to keep a journal of cloud shapes. These cloud studies can be done in a few minutes apiece. Start to identify cloud types and increase your cloud IQ. As your interest and curiosity grow, your ability to see and render clouds will improve dramatically.