To learn how to do something, make it easy enough for yourself that you can have fun with it. When it becomes so easy that you become bored, you will naturally want to increase the challenge. If you let the natural learning process proceed in this way, your skill will progress automatically, without a sense of conscious striving. In tai chi this is codified as the 70% rule: when practicing tai chi, exert at no more than 70% of your maximum capacity.
To speed up, slow down. To learn fast, train slow.