While this guide was written for musicians—the concepts are quite applicable to visual artists. There is a slight bit of misrepresentation in the beginning regarding the work of K. Anders Ericsson (placing more emphasis on the 10,000 hours rather than the content of practice time—a pet peeve of mine), but I assure you that some great tips for deliberate practice follow.
"Does it ever feel like in spite of all your hard work, you’re not progressing as rapidly as you should? Or perhaps you’ve hit a plateau and can’t find a way to get to the next level?
It’s not just your imagination. And don’t worry – it’s not a sign that you’ve reached the limits of your ability either. Not by a long shot.
The truth is that not all practice is created equal. Some approaches are much more effective than others." -The Bulletproof Musician