If you have difficulties with (German) grammar, there is one good idea to progress faster:
WRITE 
When you speak, you generally don’t have the time to meditate about correct grammar structures. But writing even a short text, you can take the time you need. Later on, you’ll get the corrected journal back, sometimes with some remarks. Then you can check your errors, and you know where to focus on.
So, make good use of the writing tool! You’ll see your progress!
This is a really great advice! I’ve recently started to use this tool more actively and there’s always something new for me to learn. Even though it’s better to remember the right version of something from the very beginning, it’s never too late to relearn it and start to apply it correctly.
I totally agree. Listen and reading is more passive learning, while writing is more active! 
By the way:
There are many writing exercises linked with videos or texts in your self-study. But you can always make writing exercises without a necessary connection to a video topic. Just write what you’ve done today or whatever you think - we’ll correct it!
As the writing exercises are currently limited to 150 words, you can write longer texts using https://go.chatterbug.com/. This is very helpful, when you want to write a letter or mail in German and you need correction.
Thank you for the advice @SKrausser! I do find the corrections very useful, and it helps me to understand why and how I had made the mistake.
I totally agree that writing is a completely different ball game to speaking. When speaking, I am actually able to mumble words in such a way that it sounds correct. 
There is no hiding when it comes to writing! 