I would say practice, most likely a job that requires you to type a lot. I remember that my typing speed was a lot higher around term paper deadlines or whenever I got halfway serious about modding or programming, but it's one of those skills that quickly diminish unless used constantly.
It's not work, because I've only gone up ~5 words/minute during my working years.
The vast majority of my speed increase (up to 78 words/minute) came in high school, where we were forced to repeatedly type out page-long passages and start over if we made a mistake. That technique forced me to cognitively focus on each key. I basically have two typing conceptual frameworks:
1. I think each letter as I type it: I still fall down to the 60 wpm range doing this exclusively, but I virtually never typo.
2. I think words as I type them: For common forum posts and most of the words on that list, I have typed the word enough times that I can think of it as a word and type it without thinking about the sequence, similar to one button but pressing several.
Over the years I have gotten better at switching between the two also.
The high school class also helped because the school's eventual valedictorian (this was a freshman class, and the start of a long rivalry) was in that class too and wanted to be the fastest typist in there, and I wasn't having it. We traded off who was faster, and in the end I beat her by 3 wpm. I got a comment about that in my senior yearbook lol.