Willpower has become one of the most intensively studied topics in social science. Researchers around the world have found that improving willpower is the surest way to a better life.
While self-esteem is fundamental to our personal welfare, I believe, as researcher Baumeister exposes in 
Willpower that major problems, personal and social, center on failure on self-control: compulsive spending and borrowing, impulsive violence, underachievement in school, procrastination at work, alcohol and drug abuse, unhealthy diet, lack of exercise, chronic anxiety, explosive anger.
Willpower look much more than a metaphor
Researcher Baumeister has arrived to the conclusion that willpower is like a muscle that could be fatigued through use and warns us:
If you’d like some advance warning of trouble, look not of a single symptom but rather for a change in the overall intensity of your feelings.
If you find especially bothered by frustrating events, or saddened by unpleasant thoughts, or even happier about some good news—then maybe it’s because your brain’s circuits aren’t controlling emotions as well as usual.
Ego depletion thus creates a double whammy: Your willpower is diminished and your cravings feel stronger than ever.
sorts out four different types of willpower and suggests to stick to one challenge since you have only one supply of willpower.
We can divide the uses of willpower into four broad categories: control of thoughts, control of emotions, impulse control, and performance control.
Emotional control is uniquely difficult because you generally can’t alter your mood by an act of will. You can change what you think about or how you behave, but you can’t force yourself to be happy. To ward off sadness and anger, people use indirect strategies, like trying to distract themselves with other thoughts, or working out at the gym, or meditating. They lose themselves in TV shows and treat themselves to chocolate binges and shopping sprees. Or they get drunk. We can’t control the impulses, which is what most people associate with willpower, but how we react. Performance control is focusing your energy on the task at hand.
Glucose depletion can turn the most charming companion into a monster. The old advice about eating a good breakfast applies all day long, particularly on days when you’re physically or mentally stressed.
If you have a test, an important meeting, or a vital project, don’t take it on without glucose. Don’t get into an argument with your boss four hours after lunch. Don’t trash out serious problems with your partner just before dinner.
The result of conflicting goals is unhappiness instead of action, as the psychologists Robert Emmons and Laura King demonstrated in a series of studies.
By asking people about their goals and then monitoring them, the researchers identified three main consequences of conflicting goals:
First, you worry a lot. The more competing demands you face, the more time you spend contemplating these demands. You’re beset by rumination.
Second, you get less done. It might seem that people who think more about their goals would also take more steps to reach them, but instead they replace action with rumination.
Third, your health suffers, physically as well as mentally.
The link between willpower and decision making works both ways: Decision making depletes your willpower, and once your willpower is depleted, you’re less able to make decisions.
If your work requires you to make hard decisions all day long, at some point you’re going to be depleted and start looking for ways to conserve energy. You’ll look for excuses to avoid or postpone decisions. You’ll look for the easiest and safest option, which often is to stick with the status quo: Leave the prisoner in prison.
Emotion regulation does not rely on willpower. People cannot simply will themselves to be in love, or to feel intense joy, or to stop feeling guilty. Emotional control typically relies on various subtle tricks, such as changing how one thinks about the problem at hand, or distracting oneself. Hence, practicing emotional control does not strengthen your willpower.
The key is to concentrate on changing a habitual behaviour.
One simply way to start is by using a different hand for routine tasks. Many habits are linked to your dominant hand. Making yourself switch to your left hand is thus an exercise in self-control.
Another training strategy is to change your speech habits, which are also deeply ingrained and therefore require effort to modify. Break the adolescent habit of peppering your discourse with ‘like’ and ‘you know’ constantly.