This is contest judging season. One recent contest entrant wrote, "She looked away in discuss," when the author meant disgust. Spell checker doesn't catch this kind of mistake. Another pair of eyes perhaps would.
Updated software versions make a writer's life easier. I often type it's when the apostrophe is not needed. I turn on the 'Non-Print Formatting Characters' when I write. My word processing software underlines anything the software authors consider a problem. If I've typed it's and should have typed its, a little green line shows up under the word. All I have to do is figure out why, and correct my mistake.
Learn to use all the features of your software. Then, as the final step before submitting your manuscript or posting a blog, ask a trusted reader to read what you've written. Not a sister or good friend. Find someone who knows mistakes creep into our writing like ants sneak into my house on hot, dry days. Your job as a writer is to identify the mistakes on a written page and eliminate them from the printed page.
Twice while writing the paragraph above a little green line showed up, once to show me I'd pluralized a word that didn't need it, another time to show me to add an s to a word that should have been plural. Trust your software.
Let's see if my software catches a mistake in verb tense. He look at her with a question in his eyes. Yes, a little green line appeared beneath look to show me there is a problem. If I make the present-tense verb past-tense, the green line goes away. I often see the wrong tense of verbs used when I'm judging manuscripts, and most often with the word look, perhaps because this word is often overused.
The ease with which a word processor allows a writer to revise a sentence can also shoot you in the foot. Watch out for mistakes in verb tense.
In writing this I noticed a green line I could not explain beneath a word followed by a comma. I deleted the comma and the green line went away. I'm not sure I trust my software that much. I'd rather have too many commas than not enough. I want the reader to understand what I've written, not have to go back and read the sentence again to determine the meaning.
So, update your software, find a trusted reader you can depend on to find the numerous typos, missing words and punctuation errors we all make.