How To Edit A Scan

So the secret of brilliant scans is two layers in multiply and darken? Or is there more steps you would recommend for enhancing scans?

I'm searching desperately for a scanning tutorial especially for finished drawings, but I have no luck so far. There's a lot of hints about cleaning sketches (using "levels" mostly), but what do you do with a drawing, which contains subtle shading and therefore is much more difficult to "fix" after scanning? That's what makes me wonder for a while now.

Thx for your advice in advance