Avoid Smudging Your Work
When you are working on a large drawing and need to draw in one area of the paper, make sure you first cover the rest of the drawing with a second sheet of clean paper to rest your hand on. If you rest your hand on your drawing without the paper, you will smudge it.
Clear Any Eraser Shavings
The little bits of rubber which collect on your paper whenever you use your eraser can easily ruin your drawing if you do not clear them off the paper. The smaller shavings can be difficult to see and if you unwittingly grab a tissue and begin to smooth out some graphite and pass over the eraser shaving, those shavings will collect on the tissue and will erase any part of the drawing they come into contact with.