a couple of tips (at least these work for me and my particular combination of scanner and software - ScanMaker X6EL and PhotoShop or Corel PhotoPaint)
If you have a lot of white/light areas in the art, set your brightness a couple notches lower on the scanner software. Otherwise, any detail you might have in that light area gets completely lost. You can always lighten up where needed with your photo editing software.
Play with the contrast settings in your photo editor. I find that most everything loses some contrast in scanning. The darkest darks and lightest lights get lost. Your contrast settings should show a histogram (graph) of some sort, tweak the outermost sections - this'll bring back your darks and lights and won't affect the mid-tones too much.
For graphite drawings, scan as color and then convert the image mode to duotone (a combination of 2 colors), using the darkest black in your palette (I use Black 6 CVC 2X from the Pantone palette) and a yellow (I use Process Yellow CVC) to give it a warmer tone. I always have to adjust the color curve afterward to tone back the yellow quite a bit. Then you'll have to convert the duotone back to color to save as a JPG.
I scan at 500 dpi 'cause I often make cards/prints of my ACEOS. After I color correct, then I resample to 72 dpi and save that as a new file. If you scan at low res, you won't have the option to do much else with the image except post it on the web.
And if you have a little extra money to spend, get a "Huey" monitor color calibrator. They're made by Pantone, easy to use and they do a good job of matching your monitor to reality. They're under $100 and available on-line - just google "Huey".
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-Ann
"Anyone who considers protocol unimportant has never dealt with a cat." -- Robert A. Heinlein
-Ann
"I have got pepperoni. Wherever it lands, that's where the miracle will happen." ~ Gary Busey