Repositories are awesome, and we should have more of them.
I recently completed BJ Fogg's Tiny Habits, and it's a pretty lightweight way to install new habits (recommended). However, I realized I could use a better repository of useful habits.
So, please use this thread to suggest habits that you've found useful. Bonus points for evidence/anecdata of usefulness.
Obviously, 1 habit per comment makes upvotes a clearer signal of collective approval.
Meta habit: Every time you want to install a new habit, make an Anki flashcard for it.
In the beginning phase, while you install the habit, the card will be asked frequently. Later on, when you are less likely to forget the habit, it will be asked for less frequently. If you recently failed to follow the habit you can click "again" when the flash card is asked.