I use a keyboard with a very light and springy feel, and low travel. It also helps to not think of individual letters but rather entire words, so you can be pressing multiple keys nearly simultaneously and "buffer" multiple words ahead.

(You'll know that you're buffering when you take a typing test and by the time you see that you've mistyped something you've already typed several more correct words, so it pays to be accurate before you try to buffer ahead.)