1) Don’t allow yourself the ‘luxury’ of mistakes. Mistakes cost far too much time to repair and only create uncertainty, whereas your practice ought to build security. Remember, your performance is a direct result of how you practice, and efficient piano practice means playing correctly. If you start making mistakes, it means either that you’re going too fast to learn the music or that your brain is tired. If that’s the case, it’s best to take a break and do something—anything—else.
2) Study away from your Instrument. Some of the most efficient practice can be accomplished without an Instrument. Analyze the piece, listen mentally, hear each voice in your inner ear, sing each line, discover thematic relations and harmonic subtleties. It is always amazing to me how many music students simply learn notes without ever really knowing the piece or its compositional strategy. Instead, be sure to make mental study and analysis an integral part of your piano practice.
3) Practice slowly. It is a known psycho-physiological fact that the brain cannot absorb musical information in detail when playing fast. It is therefore essential to work slowly and carefully at all times. Never try to force speed, as such attempts are harmful both to the memory and to acquiring velocity.