Pencil work can be extremely messy, no matter what type of pencil you use. Even colored pencil will smudge or get on your fingers if you lean on it. I wrote a short post last year about how easy it is to get fingerprints on your charcoal drawings. While searching for a good topic for a new drawing tip, I realized I have let this topic go too long.
The key to not ruining a drawing by smudging is, of course, prevention. There are many steps you can take from start to finish to ensure you keep your fingers off your paper. As I mentioned in the fingerprint post, just handling your paper before you even start can lead to fingerprints on the finished drawing. When I tear the paper out of the pad, I wear disposable cotton gloves. I also wear them while laying out the sketch, because I tend to touch the paper a lot. Once the paper is on the easel, I leave it there until it is finished. The less I move it around, the less chance there is to touch it accidentally. Once it is on the easel, I also do not tape it down since even artist's tape will leave gum residue that sometimes cannot be camouflaged.
So you're finally sitting down to a nice, white sheet of paper. What happens when you start to draw? If you're right-handed, you could draw left to right, top to bottom, to avoid touching areas you've drawn already. This is usually not feasible, however (I mean, who does that, anyway?). The key is to put something over the parts you've drawn so you don't stick your hand in it when you draw on the other side. To avoid touching the paper altogether, I do this even with the blank paper. So what do you use? Find a piece of paper, preferably acid-free but newsprint or tracing paper will do, that is larger than the drawing paper, and lay it over. I don't tape mine down, but if you do it is less likely to move around while you're working, which can smudge your drawing.
Finally, there are sprays you can use to "fix" the charcoal or pencil in place. I use Krylon Workable Fixatif. The sprayed areas of the drawing are then resistant to smudging (not completely smudge-proof), and you can still use erasers and draw over it. Then you can spray the whole thing when you're done. There are many other sprays that are only good for finished drawings.
Ultimately, it takes a little effort, but the results are well worth it.