Dive deeper into your target language. Learn about the theory, browse cheat sheets, and pick up interesting tips and tricks.
You can write pages to practice your writing. You can review cards to practice your vocabulary. You can combine the two to learn from your mistakes. But, at some point, you will also need to set some time aside to study the theory.
I decided to write about my own learning process so that hopefully others can benefit from it as well. Since it’s just me for now this will initially only be about Spanish, but I hope that, eventually, other languages will follow, perhaps from other enthusiastic users.