Elaborate on your sketch. Use heavier/darker line to bring out the parts of the drawing you need, and use an eraser to take out the lines you don't need. Add details, bit by bit, making sure to frequently step back and look at your drawing as a whole to make sure it's coming along the way you want it to. Learn and experiment with several techniques, which can enhance your ability to express ideas through drawing.
Draw with shading. Shading means the differences in light and color. Think about the way the light hits an object and which parts of the object are light or dark as a result. This can add luminosity, intensity, and depth to a drawing.
Picture a bowling ball in the foreground and the sun, right as it's beginning to set, in the background. Since the sun is close to the horizon, the light is going to be hitting the bowling ball from a very low angle, as opposed to high angle (where the sun would be at around noon on a sunny day). This means that in order to capture the light hitting the bowling ball, you're going to need to shade the top of the bowling ball lighter than the bottom, because the sun won't hit the bottom directly.
Practice with the shadows. If you want to get very realistic drawings, study the way that light reflects from objects, including the shadows that it leaves. Shadows can be almost mirror images of the object, or they can be stretched out, diagonal, and distorted. Pay attention to the type of shadows that the sun makes in real life, and try to duplicate that in your drawings.