Reading widely and often is the key to writing well.
If you want to develop your writing voice, you have to read a lot of good books.
If you want to write well without thinking about the mechanics of characterisation, dialogue and plot all the time, you have to read a lot of good books.
If you want to write strong, comprehensible prose without having to check your spelling, grammar or punctuation after every sentence, you have to read a lot of good books.
I’ve written a few posts about how reading helps writers, which you can read here. There are all sorts of “how to” books which can help you develop specific skills: you’ll find some of them in my bookshop, here. But if you want to develop an instinctive understanding of how writing works, the best way to do it is to immerse yourself in the best writing you can find.