How many hours a day should 

I be practicing? 

This article talks about the difference between mindless practicing and deliberate practicing. It is hard to make the switch over and trust that it is the better way, but in the long run it is well worth it! This mindset is something that I'm working really hard on in my studio right now. More often than not,I'll get a sigh or eyes rolled if I tell the student he/she gets to do one of the repetition games I have. After we do a few repetitions of deliberate practice, they hear the difference and are satisfied with the work they have done.