When my fingers hurt after too much time on the keyboard, I... take a break, wash my hands in cold water and massage them with hand lotion.

My tip to improve your typing speed is to... fine the patterns of mistakes that you often make, and improve on those. For me, for what ever reason, it's the word "practice". I always want to make the p, a capital p, even if it's the middle of the sentence. It took a while but the sensation to do so is slowly going away.