Scanning pencil sketches

I do a lot of pencil and paper wireframing and would like to be able to faithfully scan my sketches. All my scans and photos have been terrible and I wonder if anybody else has faced and solved this problem.

EDIT:

Here's an example. This was from a page with a series of sketches using different graph types. I use mechanical pencils - 5mm and 9mm thickness in both red and black. The 9mm black comes out (poorly) and the 5mm red and black details do not appear at all.