I've always used pattern paper. It's like really thick interfacing and having tried tracing paper, plain interfacing, and other substitutes, I feel there is no substitute for the good stuff. I think it's called swedish pattern paper or something. I use a fine tip sharpie to trace the size I want-then I mark the pattern pieces with the name of the piece, the size, and the pattern name/number. When I'm done with it I save it in case I want to make it again in that size.