Hiya!
When it comes to learning words, I recommend using either Anki or Quizlet to make flashcards.
I usually prefer Anki, but this is a personal choice. They both have different advantages and disadvantages. Explore!
As for grammar, just learn that stuff off by heart, when you've learnt some basic vocab.
In English, you didn't know how to say 'I ate the dinner' until you've learnt these individual words first.
Don't try to rush yourself. If you're using Duolingo, don't XP farm, even if it may be tempting to. And try to not use ONLY Duolingo. You may want to only use Duolingo, for the XP, but, as great as Duolingo is, it has faults. I like to usually use sites which are specific to the languages I'm learning. Despite learning languages daily, I struggle to keep a streak of 3 on Duolingo, because it's not my main source of learning.