Fowler's book (The King's English) is old but still worth having IMO. You can find it for free online. I recently heard very good things about Carter and McCarthy's Cambridge Grammar of English. They include material based on how it's used by people in the real world and cover any nuances one might come across.
see spag list i started that is now a sticky: https://www.writingforums.org/threads/writing-basics-reference-sites.21049/ and a more general one from ferret: https://www.writingforums.org/threads/writing-resource-links.4675/