Below is my post on WILLPOWER. In addition, be sure to see my SPECIAL MESSAGE TO MY READERS about changes in my blog this year.
For many people willpower does not work when trying to change their behavior. Why is that?
One part of our brain tells us do whatever makes us feel good, rewards us, or at least keeps us from feeling bad. Because changing a behavior causes us to be uncomfortable, this part of our brain tells us not to change. To resist this message from our brain we need to make the old habit more difficult or the new behavior easier. For example, if you want to change eating patterns, removing certain foods from the house makes the old habit harder than eating available healthier foods. If wanting to reduce spending, not having credit cards in your wallet makes spending harder than spending only what you can immediately pay for. 

When wanting to change your behavior, it is best to trade something new for the old. For example, if your goal is to reduce time on your phone (old habit), you can select a different useful or enjoyable activity to do (new habit) when you would normally spend time on your phone.
New replacement behaviors need to be turned into a habit. Building a habit takes repetition over many days, usually several months. It can be helpful to add the new habit to another routine you are used to. For example, if wanting to floss your teeth regularly, adding flossing to your existing teeth brushing routine will help make flossing a habit. You would be adding a new behavior piggy-back to an already well-established habit.
Tracking and rewarding your progress also helps turn a behavior into a habit. For example, you could keep a roll of quarters near your bathroom sink and put a quarter in a jar every time you floss. When you have enough quarters, treat yourself to one of your favorite foods.
When you feel uncomfortable while trying to change behavior, remember you are a good thinker. Whenever you have the urge to keep doing what you want to stop doing, think about why you want to stop. This can slow you down and help you face the facts about the bad part of an old habit and the advantages to changing to a better behavior.
For more information about changing habits: THE NEW SCIENCE OF CHANGING OLD HABITS by Leslie Goldman