If you read Charles Dickens or Jane Austen, the words are pretty flowery and formal, and I think that's confusing to writers who live in the now. Because you have to remember one important thing when you're writing: readers are your friends.
Did We Just Become Best Friends?
Books are not the place for you to be formal. You can do that on Twitter, if you want. I've long believed that we could use a bit more formality on social media, but books are intimate. You're putting your soul on the page, and somewhere out there some individual is reading those pages that represent your tears and sweat and missed sleep. So I don't want to see formality in your books. That's where you want to be casual, and treat the reader like they're actually your close friend...because now, they are.
Taking a casual tone in your books is often much more effective than all the flowery, formal language in the world. When you're reading the classics, it's important to remember that they sound very fancy now, but back then this is the way people actually talked. So when you're narrating your books, write them the way that you would speak them. While you're writing, imagining that you're telling the story to your closest friend. Write the book as if you're addressing them. Write it in your own voice and in your own tone, and you'll find that you're doing some of your best possible writing.
Readers are your friends. Write your books with that in mind, and they'll start to feel that friendship while they're reading your work. It's much easier to lose oneself in a casual piece of writing, a piece of writing that feels friendly, than it is to get lost in something formal and cold. So be friendly, and your readers will be more apt to treat your books like their friends.