Anki is software that helps you remember things. It is used largely by people with idiosyncratic and extreme self-development goals. Much of what you can read about Anki therefore recommends idiosyncratic and extreme behavior.
But we all want to remember at least some facts: that thing we keep needing to look up at work, our cousins' birthdays, or whatever. And Anki is the most efficient way to remember facts. So Anki is useful for just about anyone.
That argument is the memory-management analogue of "if you can't afford a good lawyer, you certainly can't afford a bad one." If you don't want to spend effort memorizing things, software that minimizes the effort per thing remembered is what you want, even if other people use the software to increase the denominator when what you want is to decrease the numerator.
- Don't worry about duplicating cards. You'll simply see each of the duplicates less often, and this will approximate there being just one card with that information. It's probably better to have cards duplicating information but presented slightly differently, so that your brain doesn't latch on to the presentation so easily.
- All else equal, switch up the physical context in which you study cards (again, to encourage your brain to learn a connection between a prompt and a fact, not a connection between some wallpaper and a fact).
- I like using fewer decks, more loosely organized, so that (i) I don't spend as much time clicking between decks and (ii) there are fewer accidental patterns in the clustering of cards I review.
- When I'm reviewing a new batch of cards, I "jitter" the review times--e.g., by finding some to mark as "easy" and others not. This makes them pop back up on different days. (Adding some random variation to the review interval seems exactly like a feature Anki would already have, but I've scoured the preferences and am pretty sure it's not there.) [Update 2021-12-19: There is such a feature, and it's called "fuzz factor," and its behavior is changing. I still find myself needing to jitter things manually. Thanks to David Allison for the information.]
- Unless you are in med school or a language learner, most publicly available decks are not as good as what you can make yourself. It's probably most time-efficient to simply roll your own. An advanced clipboard manager is your friend here (and, for that matter, everywhere).
- Don't put too much information in the prompt: again, it's an invitation to form an association with an incidental pattern. This is a particular problem with automatically generated decks.