From LA 110 of AAU- how to revise a short story.

Tricks

Read your story backward, one word at a time, starting at the end. That way, you see each word separately, rather than assuming that it's correct due to context. This technique fools your mind into being a good proofreader of your own work.

Proofread a printed version of your work. Proofreading on a computer screen typically allows more errors to slip by than if you print out a copy. (Be sure to re-use the paper as scrap, so that you don't waste resources!)

Place a piece of paper or ruler under each line as you read it to reveal just one line of text at a time. This gives your eyes a more manageable amount of writing to focus on.

Read your work aloud. This allows you to hear the difference between what you meant to write and what you actually wrote. It also forces you to read each word individually and increases the odds that you'll spot errors.

If possible, let your work sit for some time before you proofread it. By approaching the writing from a fresh perspective, your brain is able to focus on the actual words, rather than assuming that the words are the ones you expect. Set the paper aside for the night -- or even just an hour.