i basically is not really pro in pencil shading but i can tell you roughly how i do pencil sketch for you to refer, hopefully help.

1) sketch outline lightly.
2) add more detail, readjust shape and make it accurately. line still light one
3) start shading, from 1 area to another area and prevent your hand smudge the pencil. from light tone to dark.

here maybe can help, try use DA search engine, got lot'sa tutorial there.

http://snigom.deviantart.com/art/Adanced-S...niques-43158629


and about your "accurately shade", at first you had to learn basics tone handling first... once you can roughly master that then you can go more complex tone.

http://shley77.deviantart.com/art/Painter-...20tutorial&qo=1


basically similar like this, just pencil must go light to darker tone lol.
digital can do reverse or whatever.

but basically my point is, understanding basic structure and tone handling, then go complex later. like dragonriene teach you.

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OFF TOPIC:
and by the way for who wanted to study colleague/ degree in art please take a look

http://adcomarttheft.tumblr.com/post/22716...tracing-copying

it is not i bashing that is not good, just their teaching method is wrong, it suppose to teach you creavity not copying blindly. even the ads also misleading too