Continually make new cards
In Anki, having a fresh stream of new cards seems important for keeping up the daily habit. I went through a period where I barely reviewed my cards at all, and the review load just piled up. What helped to kick start the habit again was a combination of a few things, including making new cards (Tips for reviving a spaced repetition practice).
(I've seen Andy Matuschak make this point or a similar one somewhere.)
See also
- Dealing with bad problems in spaced proof review
- Make Anki cards based on feedback you receive
- Make new cards when you get stuck