Atomic Habits by James Clear

I read it over the summer to help me in my own studies. Great book for as far as it goes. Granted, he's entirely secular and makes no account for sin in our bad habits or in the path for change; but as a common grace work, it's a good one. Maybe I'll post more thoughts as I have time.
@Stephen L Smith some refined thoughts.

The premise of Atomic Habits is good: Our success and effectiveness depends on the multitude of our small, unconscious habits, for better or worse. Every small good habit makes a positive contribution to effectiveness, while every bad habit has a hindering effect. The effects of habits also tend to compound over time into significant gains or losses.

You want to give attention to your habits, because they are things you do unconsciously. Therefore to fix them, you must focus on them. You want to eliminate unconscious bad habits which unperceivably sap away your gains, and create automated good habits that increase them.

The book has a method for habit fixing and forming. You strive to make good habits clear, easy, and rewarding, and bad habits to be unattractive and inaccessible.

The book also promotes "habit stacking." Habits are automated. You don't need to think about them. Therefore, when one good habit becomes automated, you can stack another good habit on top. Think of weightlifting. You work hard at the beginning just to get the form right. Once proper form is "second nature" you can safely proceed to lifting heavier weights. And so on. This compounds the progress over time as compared to always weightlifting through sloppy form.

The major weakness of Atomic Habits is that there is no discussion of sin or ethics in our habits. The tone is entirely secular and materialistic, with doses of pop brain science. The book also encourages self-focus; that is, forming your own identity, and creating habits that correspond to the desired identity. To a level that works, but a secularist is going to fall far, far short of the most desirable and "effective" identity attainable to man: a child of God and custodian of His world through Christ.

That caveat given, it's an excellent "common grace" book. I'm using it to form my own personal work and study habits.

For supplementary reading, here's a good article on the compound nature of small efficiencies.