Watch for proper subject-verb agreement. This may seem obvious, but beyond the basics, such as “Writing skill IS important” vs. “Writing skill and grammar ARE important”, it isn’t always so clear.
This is often the case if there’s a prepositional phrase somewhere between the subject and verb. It’s really easy, and I’ve done this a lot myself, to take the subject of the prepositional phrase as the subject for the verb. I’ve even seen such things slip past editors from time to time. For example, “The mother of the kittens IS grey and white”. To get rid of the troublesome prepositional phrase you could say “The kittens’s mother is grey and white.”
I think everyone hated diagramming sentences, but this is a good example where having those skills helps. Too many people think because they can talk that they can write. Thus, they “may be talking as they be speaking”. Correct grammar is important if you want to build a solid reputation as a professional writer.
A good grammar checker should pick up various mistakes including subject-verb agreement and using the wrong homonym. The finer points of grammar can get lost in a creative frenzy, plus many talented writers were bored in English class and didn’t learn as much as they should have about proper use of the language. One mistake I hear a lot is “we was”.
Another mistake waiting to happen is when a sentence has something like a preposition phrase between the subject and verb, it’s easy to mess up. For example, “He looked over his list of grocery items, which was written on the back of his hand” (correct where “list” is what “was written”) versus “He looked over his list of grocery items, which were written on the back of his hand” (incorrect, i.e. “items” isn’t what’s written on his hand).
One homonym frequently used incorrectly, which drives me nuts every time, is using shutter (a window covering or decoration) instead of shudder (to shake or shiver with fear or cold.) Look it up!
Watch for proper subject-verb agreement. “Writing skill IS important” vs. “Writing skill and grammar ARE important.” As a writer or author, knowing proper grammar is part of your job; even more so if you’re an editor.