I've been looking for the best way to communicate practice procedures for many years and have never been able to come up with just the right approach. It didn't dawn on me until yesterday that all practice techniques follow the same procedure. It's sort of like a formula which very few practice techniques ever vary from. 

Here are the basic steps in the process:

Isolate

Simplify

Repeat

Advance

Isolate

The first step is always to isolate the problems from the rest of the music. Good practicers never try to tackle all of the music at once. They do it in bits and pieces at a time. 

To someone who has never practiced this way, it may seem like a waste of time. Why spend two or three hours on two measures when you could do the entire piece of music in less than fifteen minutes? 

But the truth is, isolating the problems actually saves time because you're not wasting so much time working on music you can already play. And yes, two hours for two measures seems like a lot of time, but when you are done with that two hours, chances are that you will never have to work on them again. Not if you follow the following three steps in the process.

Practicing an entire piece every time you work on it does nothing to fix any of the problems and more ironically, it reinforces those problems each time you play the music. I think many players make the mistake of thinking that they can fix something by trying harder to play it right. But trying harder is never enough. These players will begin at the beginning, make a mistake, and then "try harder" not to make that mistake again the next time they play it. No progress is ever made this way and the end result is wasted practice time. Nothing more. 

By isolating the problems from the rest of the music, you are cutting out all of the wasted effort and focusing on those things which truly need to be fixed. 

Simplify

Nothing is gained by repeating a mistake. When you isolate a problem spot in the music, it's supposed to be for a specific reason. So you go into the next step of the process with the assumption that you can't play that passage the way it's written. Something MUST be done to make that part of the music more accessible before you begin working on it.  

There are many ways to simplify a section of music. The most common method is to slow the music down. It's typical for players who practice well to play each and every note as if it had a fermata over it. The fermata approach may seem like overkill, but it's a fantastic opportunity to focus on each individual note. You get the sound of the note in your head and the feel of it in your chops. Never underestimate the effectiveness of slowing the music down. 

But don't assume that this is the only way to simplify problem in the music. There are many different ways to simplify music which I don't want to get into here because I want this to be a general description of a general process. Let's just say that anything you can do to make the music easier is fair game. Slow it down, tongue it, slur it, sing it, buzz it, play it in a different octave, the sky is the limit. 

Repeat

Great performance is only achieved through habit. If you have a habit of playing something correctly, you will probably perform it correctly. On the other hand, if you have a habit of playing something incorrectly, you probably won't perform it so well either. Simplifying the trouble spots helps you play something correctly, but the habit isn't formed until you repeat it correctly - many, many times over. When I say that you can spend two hours on two measures, most of that time is spent in repetition.  

I often wonder what my neighbors think when I practice because playing the same notes over and over again, for hours, certainly can't sound like music to them. 

Advance

Obviously, you cannot perform a section of music in its simplified form. Repeating a simplified passage creates a habit of correct performance, but only at that low level of difficulty. The next step in the process is to increase that difficulty in gradual steps.

A good practice technique usually has two built in features. The first is a method of simplification. The second is the method of advancement. It's not good enough to practice something in its simplified format and then jump immediately back into the music as it's written. The process of getting from the simplified version to the written version of the music must be a gradual one or the process won't work. 

The metronome method is a perfect example of this process. With a metronome, you can slow a passage down to one half or even one fourth of its written tempo. When you feel comfortable with the music at that tempo, you can increase the tempo by one notch in the metronome. For most people, this increase in tempo is barely noticeable. In this way, you are able to transfer the habit of correctness to the new, slightly quicker tempo. 

Alternate

At this point, the process alternates between repetition and advancement. When you advance the difficulty to the next, slightly higher level, you repeat the passage at that level until it feels comfortable. This alternation continues until the music has reached the level of difficulty required by the written music. In the case of the metronome method, this would be the written tempo. 

Have Patience

This is not a hurried process. Anyone who advances too soon will forfeit the work they've done up until that time. If you find yourself beginning to get sloppy, it's better to take a step back and rework the previous level of difficulty than it is to rush towards the final goal.

Sometimes practicing correctly makes you feel as if the world is passing you by. If you have only a half hour each day to practice ten etudes for your lesson, spending that entire half hour on one measure may cause you great anxiety. But rushing through the music only gives you the illusion that you're getting something done. In reality, through your lack of patience, you have wasted all of that time. Then you wonder why you haven't made any progress all week.