Carla from Scientific Seamstress shares a 3-part tutorial on the Sew, Mama, Sew! blog explaining how to create downloadable patterns. From drafting the pattern, to scanning it in, to writing instructions, she covers the whole process.
Go to Part 1 to learn how about drafting a pattern and grading to create different sizes.
Go to Part 2 to learn how to get the pattern into an electronic format.
Go to Part 3 to learn about writing up the instructions and marketing your patterns.
[photo from The Scientific Seamstress on Sew, Mama, Sew!]