The best habit I started a few years ago was daily journaling. I'd tried it before with apps, or books, etc. — this time I made it the least possible effort: just a monthly entry in Notes. One word counts. Just try to always write about every day, and make up if you forget a few days.
I have a wonderful rich journal now going back years. Some days are thin, some days I have elaborate prose on some of the most beautiful or difficult days of my life. If you want a new habit, I can recommend it.