Here again, most people having used pencils to draw for any time will already have developed their own personal techniques and ideas. But here are the most valuable lessons regarding pencil drawing, that I personally, have learnt over the years.

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Always avoid resting your hand on the surface of your paper wherever possible. Your hands - no matter how particular you may be about washing them - will always be slightly greasy. Where possible I always use a second piece of paper to rest my hand on, avoiding contact with my actual drawing surface whenever it's practical to do so. Keeping your paper clean this way, in my experience helps greatly if you maybe need to erase applied graphite later (any grease or moisture from your skin effectively binding the graphite into the papers surface - making it harder to erase cleanly).
Never use your finger to smooth out shaded areas on your paper. Always use something dry to work applied graphite. You can buy proper tools for this purpose, but I tend to use cotton wool for larger areas of smoothing and cotton buds for smaller areas. Never use your fingers!
Always try to avoid resting your hand on areas already worked. Being right handed I try to work from left to right and top to bottom on my drawings. Whilst this is not always practical - using this principle as far as possible will help keep your drawing smudge free. On occasions however, resting on already worked areas is unavoidable. By using your second piece of paper as a rest for your hand however, you can get away with overworking previously drawn or shaded areas. Just ensure that once your 'rest' paper is laid on your work, you don't then, inadvertently drag it over the surface of your drawing. Lay it down, rest on it, lift it when necessary, then lay it down again, work on it again and so on - never drag it, as this can smudge any soft graphite applied underneath the paper, just as your hand would.
Always keep your harder (detail) pencils sharp. There is just no way that you can apply fine detail to a drawing with blunt pencils. I sharpen my pencils with a scalpel and then shape the lead with my file boards; this gives me a really fine point for that finest detail.
Always wipe the end of your pencil after sharpening. Particularly if you use a file board - but even if you just use a normal pencil sharpener - wipe the sharpened end of your pencil with a piece of kitchen or toilet roll before using it on your drawing again. You will always get residual grains of graphite that will stick to the sharpened surface of your pencil, these can ruin a finely drawn line, so wipe them off before using the pencil again.
Never use a 'hard' rubber on your paper if you can avoid it. All a hard rubber does is effectively 'rip' off the top layer of your drawing paper, taking your mistake with it. This ruins the smooth surface of your paper and whilst you may have removed your mistake - you've also removed your drawing surface. Redrawing or shading over that damaged surface will be very difficult. If you must use a rubber - use a putty rubber, but better by far is to use Blu Tack. Blu Tack lifts the graphite off the surface of the paper without damaging it. The more times Blu Tack is applied to a graphite line, or area of shading, the lighter that line will get.
Always clean up your work once it's finished. Once your drawing is complete clean any smudges on the paper around your work using either a putty rubber or Blu Tack, but do take the time to clean up your page before sealing your work with fixative. By removing any unintentional smudges off of your drawing, it makes it look cleaner, better defined and generally more professional.

Always seal your finished pencil drawing. Once you're certain that your drawing is complete - seal it. Graphite pencil will smudge if rubbed or touched, so seal it in with a sealing or fixative spray (Available at art shops). An alternative is a 'perfume free' firm hold hairspray - hairspray does exactly the same thing as 'proper' fixative sprays - and is cheaper too. Spray these 'fixatives' on lightly though. Too heavy an application can cause a slight loss of really fine detail with graphite work. Several light applications generally work best. Be aware though - once your work is sealed you will be unable erase any mistakes. So make sure it is right before you seal it!
If you draw yourself you will no doubt already be well aware of most of what is written above, actually much of it is just common sense really. I certainly don't profess to be any kind of drawing expert, these observations are based purely on my own limited drawing experience..............and lots of mistakes. They do however, work for me, so hopefully there may be something in the information above that may be useful to you.
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