#1: The 10,000-hour rule. Scientists have proven these are the hours required to master anything, which is about three hours per day for ten years. There's no short cut.
#2: Eliminate distractions. No TV in the background. Turn off phone and mobile devices. Ask people around you to respect your practicing time and to not interrupt you.
#3: Focus your mind. One can get more done with good concentration. In contrast, you are wasting your time if you are thinking of unrelated matters while practicing.
#4: Set specific goals. The goals can be either practicing well for a certain amount of time or accomplishing specific goals within in a piece.
#5: Listen! A musician's sense of hearing is also a muscle that needs to be developed. Listen constantly to your tone, voicing, phrasing, tempo, and music making.
#6: Slow, slower, and slower still. Most musicians have found that practicing slowly helps immensely with learning a piece of music and also keeping it in good shape. It takes patience and time, but you will be rewarded greatly.
#7: Physical discomfort is a warning sign. While some soreness is to be expected with certain passages, one needs to maintain a good posture and physical approach to the instrument so as to not cause any injury.
#8: Find different ways to practice the same thing. This can alleviate some boredom that is unavoidable in day-to-day practicing and also help with getting to know the music better.
#9: Get away from your instrument! One should do some research into the background of the composer and the piece, study and analyze the scores away from the instrument, and listen to good recordings by professionals.
#10: Practice performing. Playing for friends and family members before stepping on the stage is tremendously helpful.