I bought The Economist Style Guide shortly after university and I’ve used its recommendations regularly over many years. It’s had a massively positive payback for me. It’s surprisingly versatile advice, whether crafting emails, reports, proposals, or proofing the work of others.
There are several good style guides around. It might not matter which of the good ones you use. If you use one consistently, though, your writing will improve over time.
Whether this will help you in your concrete work/life for a value >17USD is another matter. Good written communication is helpful in most knowledge work, though.