It happens largely by burning common words and letter combinations into your muscles, not by stringing together individual keys. After almost 3 weeks on Colemak, I find that my most common mistakes aren't on particular letters but in particular contexts. I may get "I" right most of the time, but I still invariably type the Qwerty "I" in certain words. Because of the Colemak emphasis on digraphs, I get the feeling that as I burn it into my fingers it will make for more comfortable and smoother typing.