Our brains are actually pretty great at filling in gaps, but that's a bad thing when you're scanning for spelling errors. If you want to focus more on each word, you need to put things in reverse.
If you want to give your spelling a once over, redditor AngeloPappas suggests you read your work backwards. Going backwards forces your brain to focus on each individual word a little more since the flow of the sentences is lost.
It's a trick you'll find in a lot of university writing guides, especially since there's a lot of actual handwriting happening on campus. Yes, spellcheck exists. And yes, there are many proofreading tools out there. But you don't always have those, especially if you're taking an exam.
That said, your mileage may vary with this method. A small study from the late 80s found that reading things backwards wasn't any more helpful than reading it forwards. What mattered most was whether people reread their work at all. But what did they know? They had mullets and wore acid wash jeans back then.
Try reading your work backwards if you're concerned about spelling, but no matter what, read it over again at least once.