What really helped me improve my typing speed is...
Well, I don't actually touch type. I have my own little messed up way of doing it. My right hand does nearly all of the work, while my left hand only handles the letters u-p, j-l, n, and m. I always use my left thumb for space, and I only use the right shift key. Don't restrict your fingers to only using certain keys, just use whichever one is closest.