I don't think an author has to plan for an audio book, I would plan on getting published in print first. Trying to write a story that can be a book, a movie, an audio-book, a comic, and a Television series is adding enough handcuffs and shackles that Houdini couldn't finish a draft.
That said, if you think an audio-book is your best bet, I suggest you use the screenplay writer's trick: Read it aloud. Screenplay writers read all the dialogue aloud, and make sure it is "sayable". Some written sentences that glide by just fine, cause stumbles in speech just due to the physical movements (and necessity to breathe) involved.
It doesn't matter in reading, readers aren't reading aloud, even if they hear the words in their head, they don't encounter the physicality obstacles of actually saying it aloud.
But in an audio-book, you'd like the whole book to be "sayable," both dialogue and exposition. So read it aloud and edit until you find it all feels like natural speech.
Note that doesn't mean you should exclude words and phrases you would not SAY in normal speech. Use them. Most novels are using sentences and words we very seldom use in normal conversation. The point is NOT to make the whole book sound like a conversation you might really have, the point is just to avoid sentence lengths that leave you gasping for oxygen, and to avoid tongue twisters and words that are likely to be mispronounced, or unintentional homonyms (sound-alikes) that could be misinterpreted.
But I would also presume an audio-book will be voiced by a professional trained voice (actor or speaker) and they know the tricks to make things sound clear. (You can practice this if you want with voice recognition on your phone, and seeing which words it confuses for other words -- You are not saying those words clearly).