Being able to create effects of light and shadow is tremendously important in drawing. Even if you never attempt to draw and shade folds of fabric (which is a challenge, trust me), you still need to be able to make simple effects that will suggest light and shade to a normal viewer. This takes practice.
There is a classic exercise for shading that will give you some excellent practice. It is so simple that many people dismiss it, and never actually do it, but if you become one of the students who does actually start and complete this exercise, you will have improved your shading skills dramatically. Do the exercise more than once and you will reap further benefits. Do it a third time and… I’ll let you guess what happens.
The exercise is to get a plain sketchbook, a simple drawing pencil (any #2 pencil will do) and an egg. If you do not have an egg, a large smooth stone like a river stone will do. Even a ball with a smooth surface will work. Having a good eraser (like a kneadable eraser) is helpful, but not necessary.
You sit down and begin drawing your egg, but you may not make any lines. You are forming this image of the egg purely with shading. You will probably have a few false starts, but don’t worry about that. Just crumple up your mistakes and start again.
As you really settle into doing this, you will immediately realize it is much harder than it sounds. Here are some hints. First, you can use the side of your pencil to create a wider, softer “line” or mark with your pencil than the tip will make. You can also use the tip of your pencil to create extremely light lines that blend together to make the shadows of your egg. You can even make your shadows using “cross hatches” which is when you make a series of light parallel lines in one direction, then make another set of lines over the first set, but at a 90 degree angle. The overlapping sets of lines create the effect of a very light woven pattern.
When you are really good, you will be able to show the little bumps and pock marks in the egg with your shadows. Most people just ignore these little imperfections the first time they do this exercise.