This method disconnects it from your normal language processing. Start by learning simple words so you associate it with your language. You'll be at 20wpm no time.
Looking in to it, I see there's two ways - Farnsworth & Koch. The downside of the former is that you get stuck with slow speed and have a harder time to get faster. The downside of the latter is that the initial learning process seems more pointless because there's no actual words.