Sharpening Drawing Pencils
When sharpening your pencils for drawing, use a craft knife (carefully!) Rather than a pencil sharpener. You can get a longer, more effective point on the pencil this way and you can also shave it to a chisel edge which gives you more options for creating different line widths and textures. This works for pencil crayons, watercolor pencils and pastel pencils, etc. as well as normal graphite pencils.
Conserving and Using Putty Erasers
Putty erasers are excellent for drawing, being much softer and gentler on paper surfaces – especially watercolor paper – than regular erasers. They're readily available from art supply stores. However, they're a bit more expensive than ordinary 'school' erasers – but of course, just as easily mislaid.
The larger size of putty eraser is usually about 2 "x 1.5" so I cut or tear a new one into four smaller pieces and use one at a time. In reality, I rarely get through one piece without losing it and I have found through painful experience that is it's just as easy to lose a large eraser as a smaller one.
You can use a putty eraser by rubbing it on the paper in the normal way or use a dabbing action to lift out pencil marks. Its biggest advantage is that you can mold it to a very fine point or chisel edge if you want to remove part of an image without affecting the immediate area around it.
Cleaning a soiled putty eraser is even easier. Just pull and mold the dirty edge inwards, until a clean area appears. You can do this for quite a while before before up every clean bit.
Cleaning Pencil Erasers
If you use any other sort of pencil eraser such as the plastic or the plain old school 'india rubber' type, it's easy to get a dirty residue on your paper if you're not careful and the devil to get it off, especially if the eraser is colored.
The two main problems are that you either pick up pencil residual from erasing previous items, which then transfers to your paper next time you use it.
Alternately, if you've not used it for a while, the rubber surface oxidises and will badly smudge your paper. To solve this problem in both cases, simply rub the eraser on a handy hard, smooth surface – a drawing board or worktop is ideal.
This cleans off the residue and leaves a nice clean surface on the eraser. In fact, it's a good habit to clean your eraser when ever you pick it up so as to ensure your work lasts clean and tidy through your drawing session.
You can also shave off a sliver of the plastic or rubber eraser with a craft knife and use it to pick out small areas. But see the reference to putty erasers above.