How to build a habit that holds

I have started and lost more habits than I have kept. The ones that stuck were embarrassingly small at the start.

Make the first version too small to skip.

One page, one set, five minutes. The point at the start is the streak, not the volume. Volume is a problem for later and a nice one to have.
Attach it to something already fixed.

After coffee, before the shower, on the train. A habit hanging in open time competes with everything else and loses.
Same time, same place.

Deciding when to do it costs willpower you could spend doing it. Remove the decision.
Make it visible.

A calendar, a note, a tick. You need to be able to see the run of days, because the run is what you protect.
Never miss twice.

One missed day is life. Two is the new pattern. This single rule has saved more of my habits than any amount of motivation.
Reduce it on bad weeks instead of stopping.

One page instead of ten. Keeping the thread costs almost nothing and rebuilding from zero costs weeks.
Pick the version you can do at your worst.

Design for a tired Tuesday in February, not for how you feel on the first day.
Do not stack three at once.

One new habit at a time. Three simultaneous changes is a plan for a specific kind of person, and most people never is that person.
Expect the first month to feel like nothing.

Because it is nothing, measurably. The compounding starts later, and quitting during the flat part is the normal outcome.
Tell one person.

Not an announcement to everybody. One person who will ask how it is going in a fortnight.

Make the first version too small to skip.