My teacher passed down to me a quote from his professor a week or so ago:"If you hear someone in a practice room, and they sound good, they aren't practicing."More or less, you should be focusing at least 80% on the things you're doing poorly.
You might also try studying your music away from the piano. I have found this method extremely effective when learning new pieces. It is very difficult to do in the beginning but once you're accustomed to it you'll be able to memorise about a page of music a day. You won't necessarily be able to play that page but at least the notes will be in your head.