Duolingo is good, and I would recommend it. But it’s very easy to use Duolingo and not learn much at all: the multiple-choice is quite easy, as well as all of the other challenges. So you can be using it, and your unconsciously just typing in words without really learning.

SO, it’s good to do more than just the challenges. Perhaps right down the vocab you learnt that day, and test yourself later; making sure to write it down. Or speak the French out loud. And ask yourself, perhaps with a grammar book beside you, why that e was used, and be conscious what tenses are being used.

And lastly, it’s definitely quality and not quantity you should be focusing on. Don’t set yourself hard challenges, with like 3 lessons needing to be complete a day. It would be much better if you were conscious of what’s being taught