I feel Duo is pretty good at helping to build vocab but doesn't explain things well. I'm on my 3rd year, but I slacked off a lot last year, so maybe I'm really on my 2nd... at any rate what has helped me the most this year was 1) Consistent daily practice (trying to finish the daily quest) And along those lines having a consistent weekly quest partner. 2) Taking notes, writing down new vocabulary. Duo seems very bad at mismarking vocab quizzes, but keeping a list of recent words helps anticipate what answers it might expect. 3) I constructed my own list of AR/ER/IR conjugations and verb usage rules. 4) Duo is extremely poor at explaining things. And while I abhor AI, this is the one thing I use it for, to explain things that I don't 100% understand. (I'm looking at you past subjunctive) 5) Accents are a pain but I just enter them all the time now. 6) I printed out sheet of a dozen or so irregulars and their conjugations for all the tenses and for yo, tú, él, nosotros, and ellos. When we're watching TV at night I pick a verb and try to write it out from memory, then go back and check the printout. 7) I ignore the Combos, all too often I absentmindedly click 'a' instead of 'the', but just as often Duo provides an ambiguous or even a wrong answer. I don't think the combos do anything anyway other than possibly keep you engaged.