If your goal is to have something to pull out on the bus and learn about another language Duolingo isn't bad.

It's pretty bad for fluency though.

I recommend a method called comprehensible input. Basically, all you do is watch, listen, and read in French - totally in French, no translations whatsoever. That sounds intimidating, but the beginner stages they really talk at you like you're a baby almost. They talk with their hands a lot and use drawings. That's the most important part, because in the beginning you won't be able to understand any French or hardly any. But by making it so simple you can basically understand even though you don't know the words. After a hundred or so hours of this, you can move on to slightly less easy content. And so on and so on until you can understand just regular media in French. At that point, your learning will really take off, because you can watch things that you're actually interested in and that will capture your attention more.

You generally won't do any explicit grammar or vocabulary practice. That's on purpose, the arguments of comprehensible input is that language isn't learned, it's acquired. You didn't learn English by rote memorization, you listened a lot. If you can hear a few words and make the connection to the meaning by watching, and then you hear that word dozens or hundreds of times more - you will have a better understanding of that word than a simple translation flashcard could ever give you. Because words don't have just one meeting they're complex and change in different situations. But the best part is through this method you won't even realize that you're learning these words. Same goes with grammar, with this method things just kind of sound right. You can use the correct grammar, but you might not necessarily be able to explain why. Just like native speakers. That's how I've been learning Spanish.

I've personally listened, or watched over a thousand hours of things in Spanish in a bit over a year. And at this point most media is almost as easy to watch as English for me. I also read the full Harry Potter series in Spanish. (It was rough at first, but after I got used to the writing style a lot of the times I'd forget it was in Spanish in the more exciting sections) I need to practice speaking more, I can definitely do it and be understood but it lacks pretty significantly behind my understanding but that is really just a question of how much practice I can get. But once you've banked 1k, 1.5k hours the rate at which your speaking will improve is way faster than the process of learning so far.

Check out this this playlist of videos that really explains things in more depth. It has English subtitles you'll have to turn on. (Audio is Spanish) https://youtube.com/playlist?list=PLlpPf-YgbU7GrtxQ9yde-J2tfxJDvReNf

I've tried to learn French, german, and even Spanish before but until this try when I discovered this method, I didn't really get anywhere. At this point I'm almost comfortable saying that I'm bilingual. And it really doesn't take that much effort just make it a routine, and once you can get into more advanced and interesting videos just watch things that you're interested in. When you really get good, you can just watch the TV shows and movies that you already like to watch, but put on the French dub. It's that easy. I'm not doing anything differently now than I was before I knew Spanish but I'm learning every day because I just do the things I normally did but in spanish!

For French I don't think there's anything quite as central, large, or organized as Dreaming Spanish - but there are many smaller French channels trying to build up and plenty of reddit threads with compiled resources for learning French through CI.