How can I improve my English by reading books?

I love reading, I tried to read everyday. Mostly thriller or mystery but I start liking non-fiction books as well. However, despite how much I read a book, my vocabulary is still limited and my English isn’t improving. I use Libby & Kindle. So I look up the words that I don’t know. I wonder if there is a way to read a book or something I can do to improve my English. Any suggestion will be helpful 🙂