How would you go about starting a font design?

Presuming that you’re using FontLab or Fontographer (well, perhaps Illustrator) for designing—what are your starting approach? And let’s say you’re going to make a “regular” roman or sans typeface.

I’m primarily curious about technique…

Do you start off by importing an existing font, or do you start with a blank sheet and go from there?

Do you ever ‘sketch’ in one of the aforementioned applications, directly, or do you sketch each letter on paper, scan it in and, again, go from there?

I realize my question is very dependent on the project and intentions, but I’m just very unexperiened, yet curious, and would love to hear some thoughts of wisdom in the matter.