Comment by gdl

The traditional answer here would probably be to recommend the book "Elements of Style" by Strunk and White, so I'll do that in case you're not already aware of it. It's short, easy to read, and focuses on good style and common grammar mistakes. It's common as a high school or college text here (USA). From your question you seem pretty fluent already (your intro feels native or very near) so it should be well-suited for you.