I prefer to scan prints I've already finished in the darkroom. Easier to get better quality with a low end scanner for the web. My usual settings are:
grayscale mode (people go back and forth on this, but its just for sharing on the web, so it probably doesn't matter in the end)
adjust levels so the most data is captured.
tell the scanner software to save in a lossless format like .tif
In Photoshop (I don't do anything in Photoshop that over enhances the scan. Just things to make the on screen image appear the most like the already produced print)
-adjust levels/curves so the image on screen matches the print as close as possible
-apply unsharp mask - do this very subtly. It really helps scanned images pop off the screen and resemble the physical print better.
-save copy as imagename_lowres.jpg
-reduce file size for web upload
I really haven't gotten a good way of scanning negatives down. I do it on occasion, but since I don't have a finished print in hand, I end up over manipulating it in Photoshop. When I have a finished print, I already have gone through the vision steps of exposure, contrast, dodging/burning etc in the darkroom.