my friend has gay cats

My suggestions are: 

Strunk & White: The Elements of Style for grammar. There are other grammar books out there but I like this one because it’s really stuffy and strict and I trust the reader to figure out what is/isn’t worth taking into account. 

Steering the Craft by Ursula K Le. Guin: I’m going to be so honest, I have not actually read this but I’ve paged through it and it seems really good

How Not To Write a Novel by Sandra Newman & Howard Mittelmark

The Masterclass writers series is incredibly expensive but some of the courses are available through libraries or other methods

Also this is for children but Gonna Bake me a Rainbow Poem was foundational for me at ten & I don’t see why it couldn’t help someone older. 

More broadly, I listen to writers when they talk and try to pick and choose what’s useful to me. I prefer the advice of genre writers because I feel most of them really understand their craft as a craft; imo a lot of literary writers are so good at what they do they have no idea how they’re doing it. YMMV on this. I would highly recommend reading the forwards and afterwards of novels. I also like the director's commentaries of movies.

I also find instructional art resources extremely useful! Visual artists know how to describe things and imo they’re better at it than most writers. Like, here, I’ve just googled ‘How to draw light’ and this is a better description of how light affects an object than you’ll find in 99% of writer’s resources. I would also check your local community. If there are writer’s events, take advantage of them. Libraries and bookstores are good places to look. Head down to some book launches and listen to the authors talk.

Also ok this tends to be a bit of a sensitive topic online, but: if you want to improve it’s generally a good idea to seek out critique and negative feedback. A critique circle is a good way to do this. You can find them organized by communities (ex. a library, a university) or you can make one with your friends. If you’ve got people you trust, you can ask them directly to tell you what they didn’t like. I don’t know how far along you are in your writing journey — 'I did not like this' or 'I found this boring' etc might not be useful information at first but eventually it will be because you’ll learn how to identify points of friction in your own work; if you're earlier on you might need to seek out more guided critique and that is 100% fine. You will eventually get to the point where you can diagnose your own writing. (On this note: if you are posting your writing online I would highly recommend differentiating comments from critique -- I'm talking about directly solicited feedback from people who personally know you and want the best for you.)

One of my main pieces of advice is that it takes time to improve your writing skills. There are ways to improve more or less efficiently but at the end of the day time and practise is the key. It is normal to go through up and downs and it is normal to sometimes feel stuck but if you keep working at it you WILL get better. I am not a quick learner and it took me upwards of ten years before I was writing anything people consistently wanted to read BUT I see people improve exponentially faster than that all the time. Probably you will improve faster than I did. But maybe we will improve at the same speed and that is OK too. 

Other random tips: 

Do exercises that target specific skills which you are weak at 

Carry around a notebook and write down things you see as accurately as you can & transcribe conversations. In regards to the latter, would recommend developing really bad handwriting to prevent people from reading over your shoulder.