I don't use fancy drawing surfaces or pencils for my sketches, and draw very small most of the time (to save paper).  Here's an example of what my sketches look like after scanning:



I'd consider myself a sloppy sketcher.  This one is actually pretty clean compared to of my some messier ones. 

I just use a standard thin-leaded mechanical pencil, and on this particular drawing, I used some newspaper-print recycled paper.  Other times I use white printing paper or ruled notebook paper.  I use very light strokes, and don't always connect lines (not to mention double lines), so sometimes I get lost when trying to find lines for tracing and coloring.  Eraser smears and paper creases are bad too.

What I would like to know is the easiest way to trace the outline so that it converts to a decent digital drawing.  I've tried bezier lines; adjusting highlight, shadow and contrast; and polylines.  The problem with the the contrast adjustment is that the background and pencil lead are nearly the same on this particular scan, plus the sketch lines are too sloppy.  Tracing with curves and  polylines works fairly well, but it's a longer process, and I feel some lines (facial lines especially) get lost in the process, so that it doesn't really reflect the original sketch.

I'm just wondering if there's some secret I'm missing.  Ideally, I would like to merely just do a scan and convert it to an outlined digital image in a few steps, but with my drawing tools, it's difficult.

You can try inking it before you scan it in. Felt pens or pens that give out more ink will make your life easier when cleaning up the scan. But for sketches on newspaper which bleeds easily, ballpoint pens will still work fine.

And what program are you using to clean up your scans? If you happen to get your hands on Photoshop, it has features that can help with cleaning up scans. I'm not familiar with GIMP or other free programs, but the sort of features you'd want are Levels, Brightness/Contrast adjustment, and Dodge/Burn tool.