>>1159767This may sound like non-advice, but the simplest way to improve from here is to read, read, and read English literature with the mindset that you are learning. Stop to look up a definition, find out why a sentence is contructed like it is. If you are not aiming to be a professional, then that is sufficient. It feels like you're advanced enough that we're beyond basics at least. At that point there are diminishing returns from trying to plug away at guides or exercise books, or at least that's how I felt when studying English at uni. It's going to kill motivation quick.
Do still read up on grammar. Not as much for figuring out how something works in order to write/speak/understand something, but rather for subtle nuances, such as what's the difference between should and ought, or don't need and needn't. How to speak in formal and polite register, idiomatic language with phrasal verbs and sayings, etc. Stuff like that. Knowing this shit will elevate your language, but a lot of it is also honestly something that'll go unnoticed by most, even by native speakers.
Longman Advanced Learners' Grammar is one resource for that. For more basic and better organised grammar guide I've used A Practical English Grammar. You can find both online.
