I've found that using the tiny nippy cutters by Klein (designed mostly for electronic work) does good results.
I start from the cut end, working the point of the blade between two conductors and start snipping my way straight down the cord, pausing every couple of inches and separating the plastic jacket as I go along. It makes it easier if you do this cutting at two spots so you're ending with two ribbons of jacket.
I've never nicked or cut the conductors' insulation this way. It takes some practice but I've gotten pretty good at it. Take your time.
