Ask HN: How to master english language from intermediate level

Dear HN Readers, English is my second language, but I’m using it for more than two decades. I want to take it to next level where my language is good enough to write scientific journals or a thoroughly professional business documents. I know it would not be easy, but I’m drowned in various online resources. I would really love to know your advices/suggestions/comments which may help me in this regard.