Practice. Typing games, a thousand posts on here, whatever strikes your fancy. I'm still no 100-wpm touch-typist, but I know I've gotten better since I started filing a few thousand words a week. Good thing, too, since I wore the letters off this laptop keyboard less than a year after I bought it. (The rest of the family can't use it now unless they look at another keyboard as a reference. Ha. Ha. )
Then again, I know a guy who's been working at a newspaper almost as long as I've been alive -- he won a national writing award last month, in fact -- and he still hunts and pecks...