John Harkness: I found his YouTube videos helpful

I watch YouTube videos by John Hartness, publisher of Falstaff Books, and writer of The Black Knight Chronicles (among other series). He's emphasized the importance of having a clean copy when submitting to an editor, agent, or publisher. Missing commas, misspellings, and wrong words (Such as blond vrs blonde) will mark you as an inexperienced writer.

If you are going to pay good money for a professional editor, you want him/her to concentrate on character and plot development, not grammatical errors.

He recommends that all of your work go through a spell check, a grammar app, like Grammarly, and have the computer read back the text (text-to-speech), before you submit the WIP for review. I do all these things. It makes for a much better product.