There are a couple of free ebooks in amazon. I recommend youtube German with Jenny and her website and youtube German with Annia. Also in Youtube there is part of an ebook call Café in Berlin. I follow youtubers in topics I like, it has to be something you enjoy and can relax while watching.

I watch TV in German https://www.zdf.de/

I read Bild.de (a tabloid) and some blogs. There is a lot of good music in youtube, these are some songs I like because I understand them: https://www.youtube.com/watch?v=BNHamTwxJ6Q
https://www.youtube.com/watch?v=Bkj3IVIO2Os
https://www.youtube.com/watch?v=k9EYjn5f_nE

Books are always a good advise and it doesn't matter which one.

Yes, you also can rely on songs/songtexts because the language used in German songs is no total grammatical mess. (if you like Punkrock -> Die Ärzte. If you like singer/songwriter -> Adel Tawil. Singer/songwriter with German texts become more and more popular again. So, there are some. Non-Germans find Schlager music a bit strange, but if you like it, they're all in German.)

You also could listen to audio books. If you're looking for some, make sure that there's a written transcription with them.

If you search in YouTube for "Deutsch mit", you'll get a lot of channels from people who talk about vocab and grammar stuff.

Memrise is another platform that i use to practice. Duolingo is good but it's not the only thing you should use, as you know. Try to have some conversations on social media perhaps also.

Hallo!

I've just discovered the Language Transfer method by Mihalis Eleftheriou. It's free but you can donate as little as $1 per month to support the project. You can also contribute to the various language projects. Along with Duolingo I'm finding this to be a really effective method.

http://www.languagetransfer.org/complete-german

https://youtu.be/1wRGdwf7b_o?list=PLeA5t3dWTWvtU5nXIBbV1F_dy9VIyGDWb

Good luck!

If you're looking for another website to practice your skills, I 100% recommend Memrise (the official German 1-7 courses particularly). Reading is a great way to practice your skills. There are a lot of different options out there and I always recommend starting out with children's books. If you're looking for something that isn't as simple as a children's book, but that is still geared towards someone learning the language, Andre Klein's books are pretty good.