Duolingo is actually free, and it's good for practice, but there are better options. All you really need is the following:
- Dictionary (Jisho.org)
- 2-3 grammar books (Tae Kim, DoJG, etc.)
- Tons and tons of untranslated content (anything you find interesting)
- Google.co.jp (for looking up references and memes)
After you learn the kana and grammar, it's honestly just a 1-3 year grind of reading and hearing Japanese every day until you slowly "get it". The Dunning-Kruger effect is overused by people, but it does a great job showing the confidence you have after learning kana and grammar (Mount Stupid) and how it drops once you try to understand real Japanese (Valley of Despair). What matters is that you just keep reading. When you see a new word, always look it up, and if it looks common throw it into your Anki deck. Words will start reappearing and you'll recognize a lot of them, or at least realize you've seen them before. Doing this everyday is what builds your vocabulary - it's that long uphill slope on the way to enlightenment. Japanese has an especially long slope, but it's actually fun once you can read the Japanese internet and watch their videos, and it becomes a habit very quickly. For all beginners, getting to that point should be their priority. I'm no expert, but these habits helped me out a lot, and hopefully the beginner anon can find some use from them as well.