Basic Idea --
1. Have 3 options as well as 3 levels for each habit/task/project
2. The lowest (Mini) level should be something you can do on practically any day, no matter how bad things are.
3. Do the level you are comfortable with on any given day
Example (For a health habit)
Mini level: 1 pushup OR 10 steps walking OR One glass of water
Second level (forgot what he called it) : 5 pushups OR 500 steps walking OR 3 glasses of water
Pro level : 20 pushups OR 2000 steps OR 8 glasses of water.
Set the numbers that seem like no-brainers to you. This tends to work extremely well in my experience and accounts for varying environmental, psychological and physiological conditions.
The book has a points system etc which I did not find useful but is otherwise a very good complement to "Atomic Habits"