Erasers are a useful tool for lifting out (erasing) highlights and adjusting the tone of a shaded area. Try lightly erasing then shading back over in a crosshatch pattern to create texture.
I use a kneadable eraser most of the time - they pick up the graphite and charcoal without smudging. Use it in a dabbing motion. Stretch and fold it to get a clean spot whenever it is dirty. You can squish it to a point to erase small areas, with a dabbing or twisting motion.
A white plastic eraser an be used for light linework, but only if it is a smooth paper, as it tends to pull the fibers if the paper has a more velours surface, such as a soft rag paper. The pink and blue ink erasers tend to be very abrasive and tend to damage the paper. They can be used to erase real disasters, but test them on a scrap first. Really, they are best avoided.