I found this article at Life Hacker. 

Maybe you're accumulating thousands of hours of practice, but is it doing you any good? Are you working harder, or smarter? This article addresses that very question.

An excerpt is below;the full article may be read here.

A Better Way to Practice

Noa Kageyama

While it may be true that there are no shortcuts to anywhere worth going, there certainly are ways of needlessly prolonging the journey. We often waste lots of time because nobody ever taught us the most effective and efficient way to practice. Whether it's learning how to code, improving your writing skills, or playing a musical instrument, practicing the right way can mean the difference between good and great.

You have probably heard the old joke about the tourist who asks a cab driver how to get to Carnegie Hall, only to be told: "Practice, practice, practice!"

I began playing the violin at age two, and for as long as I can remember, there was one question which haunted me every day.

Am I practicing enough?

What Do Psychologists Say?

When it comes to understanding expertise and expert performance, psychologist Dr. Ericsson is perhaps the world's leading authority. His research is the basis for the "10,000-hour rule" which suggests that it requires at least ten years and/or 10,000 hours of deliberate practice to achieve an expert level of performance in any given domain – and in the case of musicians, more like 15-25 years in order to attain an elite international level.

Those are some pretty big numbers. So large, that at first I missed the most important factor in the equation.

Deliberate practice.

Meaning, that there is a specific type of practice that facilitates the attainment of an elite level of performance. And then there's the other kind of practice that most of us are more familiar with.
  
Mindless Practice

Have you ever observed a musician (or athlete, actor, trial attorney) engage in practice? You'll notice that most practice resembles one of the following distinct patterns.

1. Broken record method: This is where we simply repeat the same thing over and over. Same tennis serve. Same passage on the piano. Same powerpoint presentation. From a distance it might look like practice, but much of it is simply mindless repetition.

2. Autopilot method: This is where we activate our autopilot system and coast. Recite our sales pitch three times. Play a round of golf. Run through a piece from beginning to end.

3. Hybrid method: Then there's the combined approach. For most of my life, practicing meant playing through a piece until I heard something I didn't like, at which point I'd stop, repeat the passage over and over until it started to sound better, and then resume playing until I heard the next thing I wasn't pleased with, at which point I'd repeat the whole process over again.

Three Problems

Unfortunately, there are three problems with practicing this way.

1. It's a waste of time: Why? For one, very little productive learning takes place when we practice this way. This is why you can "practice" something for hours, days, or weeks, and still not improve all that much. Even worse, you are actually digging yourself a hole, because what this model of practicing does is strengthen undesirable habits and errors, increasing the likelihood of more consistently inconsistent performances.

This also makes it more difficult to clean up these bad habits as time goes on – so you are essentially adding to the amount of future practice time you will need in order to eliminate these undesirable tendencies. To quote a saxophone professor I once worked with: "Practice doesn't make perfect, practice makes permanent."

2. It makes you less confident: In addition, practicing mindlessly lowers your confidence, as a part of you realizes you don't really know how to produce the results you are looking for. Even if you have a fairly high success rate in the most difficult passages, there's a sense of uncertainty deep down that just won't go away.

Real on-stage confidence comes from (a) being able to nail it consistently, (b) knowing that this isn't a coincidence but that you can do it the correct way on demand, because (c) you know precisely why you nail it or miss it – i.e. you have identified the key technical or mechanical factors that are necessary to play the passage perfectly every time.

3. It is mind-numbingly dull: Practicing mindlessly is a chore. We've all had well-meaning parents and teachers tell us to go home and practice a certain passage x number of times, or to practice x number of hours, right? But why are we measuring success in units of practice time? What we need are more specific results-oriented outcome goals – such as, practice this passage until it sounds like XYZ, or practice this passage until you can figure out how to make it sound like ABC.

Deliberate Practice

So what is the alternative? Deliberate, or mindful practice is a systematic and highly structured activity, that is, for lack of a better word, more scientific. Instead of mindless trial and error, it is an active and thoughtful process of hypothesis testing where we relentlessly seek solutions to clearly defined problems.