The best course of action is to consume as much content in the target language as possible, tv shows, music, YouTube videos... Your brain will eventually pick up on certain parts of the language naturally. Also the best thing you can do is to not force yourself to speak or write in that language until you are comfortable doing so (this is one of the biggest things doulingo does wrong).

I can attest to this method working as I went from barely knowing a couple of English words to speaking it in about 4 months (you could probably do less if you stick to what I outlined above). To back up this method I suggest you look at antimoon which is written by people who have used this to learn English as well.

What language are you learning?

For me, the gameification of Duolingo pushed me away. The fact that if I fail 3 times I had to wait to generate more "chances" is absurd when it comes to learning a new language; especially if that new language is a whole new character set, like Mandarin or any Cyrillic language.

I mean yes a ton of it has to do with motivation, but the "gamification" is hugely overstated. It is incredibly, unbearably, repetitive and bland. Most people start with a lot of desire and determination, see little result for the time they put in, get bored of the same three formats of questions, then quit or just do the absolute bare minimum to keep their streak for a while before eventually missing that. The way they present the questions makes it so easy to guess that you hardly have to think a lot of times. The larger courses are so dauntingly long that once you realize how much time you're going to have to spend selecting words from a bank, clicking the corresponding icon, or typing what you hear, you become severely unmotivated.

I've tried many times. Many people I've known have been through the same cycle. I don't think I've seen it work.

This time around I wanted to learn Spanish, and tried the Comprehensible Input method. Man, for me at least, it has worked so so much better that it's not even comparable. In terms of progress, fun, and motivation it's been great for me. It basically boils down to listening to a ton of the language, but at a level you can at least follow along even if you don't know every word. You start with really simple stuff with lots of visual aids, hand gestures, repetition. After a while you move on to content with a little less aids, and shows for young children, etc. No translation or teaching of grammar.

I've been at it for about four months and have listened to over 300 hours of content in Spanish. The beginning is absolutely a slog still because at that level you can't understand much that's actually interesting, but the moment you get to the point that you can follow some simpler dubbed content and easier stuff like travel/lifestyle vlogs on YouTube it becomes ridiculously easy. You become more focused on the CONTENT than the language. Reading comes later when you've really got the sounds of the language ingrained in your brain, so you don't practice/reinforce bad pronunciation as you read.

Admittedly though, in most languages you will find it incredibly hard to find content for the very beginner level like this. Spanish has Dreaming Spanish which is a godsend, English has plenty of resources. Perhaps for most languages you'll have to use more traditional methods to work your way up to the point that you can understand. Or have a patient one on one teacher (friend) that can do what's called "crosstalk" in which you speak your language to them, and they respond to you in the language you're learning. (With as much visual aid as necessary for your level). There's been effort to create more beginner content for languages other than Spanish, but I don't think anything has touched the library of content Dreaming Spanish has yet.

At this point, I can follow most day to day conversations if they don't stray into odd topics. I can watch dubbed shows for kids/young adults (just finished Avatar: The Last Airbender) and follow enough to be more than enjoyable. News and simpler unscripted content is no issue as well. Native media, especially scripted media, is still too hard. I notice I struggle far less with abstract things other learners seem to have problems with like "ser vs estar", "por vs para", etc. One just feels more right in whatever situation but I couldn't tell you why. For only four months self-directed learning for a few hours a day I think that's pretty incredible. I can tell week by week that I'm improving.

For a more thorough explanation check out this playlist (turn on subtitles it's in Spanish.) https://youtube.com/playlist?list=PLlpPf-YgbU7GrtxQ9yde-J2tfxJDvReNf