What’s the best way to learn a new language as an adult?

I’ve been using duolingo and I can already notice a big difference in just a few weeks of time- I’m learning German for fun. It’s hard but not too hard. But I wanted to know, as an adult, what are some of the best ways to learn a new language? Do you buy a course? Just stick to the app? What seems to be the most effective and easy way for an adult to learn a new language?<br><br>*update: I appreciate all the advice and helpful information you guys have given me- I’ve put some of them into practice and will continue to do so, and thank you to everyone. Looking forward to seeing how far I can develop and progress in this journey of learning another language- I appreciate all the support from this sub, it’s been most helpful. Some of you have been very helpful to me directly- thank you for that and I appreciate it.*