Grammar is fantastic. It’s important and useful, and knowing how to use it can only make your writing stronger and your clarity of expression clearer.
But that doesn’t mean you have to follow all the rules.
If the rules are getting in the way of your ideas, if they’re keeping you from giving the impression you want to give, if they’re holding you back,
Knowing how to use the structure also means knowing when you can deviate from it.
Feel like using the nominative pronoun for subjective completion is too formal? Don’t! The range of intonation implied by the use of a question mark is too broad? Use a period.
Sentence fragments are okay. Not capitalizing things is okay. Weird syntax is okay. Prepositions at the ends of sentences are okay. All of it. It’s okay.
I would ask that you try to always use words correctly. Don’t use words for things they don’t mean. They’ll wither.
Other than that, it’s all game. Learn the grammar because you deserve to understand. Learn it, and then make the conscious decision to use it or break it whenever you need to. You should never have to sacrifice what you’re saying to fit your ideas into a rigid structure. But you should know what’s going on, and you should know why you’re saying things the way you are. Never be so lazy that you don’t bother to understand because people will understand well enough to get by. Your ideas are worth so much more than that, and you deserve to have the tools to present them exactly the way you want to.
And if anybody tells you differently, you can write them a brilliantly-constructed reply however you want.