I started off with just putting in a new vocabulary word every day and have been gradually ramping up the amount of info that I put into it. Now, I will add anything from programming details (e.g. how do you get the number of characters in a Rust string?) to key facts from the books I read (e.g. in The English Patient, who does the patient have an affair with?). My review sessions only take 5-10 minutes a day, and my only regret is not starting this habit earlier (especially in school). It's incredibly gratifying to review something, know the answer, and be very aware that without Anki, I would have forgotten it a long time ago.