When I did my Master's I had to do A LOT of written assignments. However, my writing skills were far from good. I was learning as I was writing, and I had to learn quickly. My mentor was from the U.S. and she quickly pointed out all the things that didn't make sense in my thesis.
Today, I consistently practice making sense of the information that I receive in English.
It's easy to point out what's wrong. Try to fix it, and you will see whether you actually have the skill and the understanding.
Here are the exercises that I do and ENJOY (because, honestly, fixing other people's abstracts is not a lot of fun and should be their responsibility)
1. I indulge in creative writing 2. I summarize my thoughts and experiences in writing 3. I correct my older texts 4. I read out loud (that's when I'm very attentive to the language)