Streaks has been pretty effective for me; I used it to get myself to meditate every day. There's a little detail that makes all the difference: The app shows a

Streaks has been pretty effective for me; I used it to get myself to meditate every day. There's a little detail that makes all the difference: The app shows a badge on its icon that tells you the length of your streak. Skipped a day? No badge for you. I put it on the home screen, so I get to see that badge many times a day, much more often than I would see a physical calendar.