Practice Duolingo Daily
If you practice a language or do a little Duolingo every day you will expand your vocabulary and fluency. Today, I have reached Level 23, after a long, and sometimes painful journey. Contrary to belief, I find repeating the exercises helpful as they become, over time, more tricky, so you have to think more.
I'm not as far as you, but I agree. (The number of XPs between levels increases as the level goes up. So much so that I heard level 20 is only half way to level 25. I haven't checked it, but I believe it.) It won't solve all language problems alone, but when little by little ads up over time, it makes a difference.