As previously stated, grammar has always felt tricky to me. When Roseanna and I first started critting for each other, about half the edits she did on my manuscript were commas. There were so many that the poor thing wore out on typing “comma” in the comments section, that she had to add some flare to the monotony and began saying “comma llama.” There might have even been a poem or two.
Instead of forcing Roseanna to endure manuscript after manuscript riddled with llama errors, I had her teach me some basic rules. And now I’ve invited her here to help you with your own llama issues.

Don’t forget, if you comment on today’s post, last Wednesday’s post, or next Monday’s post, you’ll get entered to win Roseanna’s Jewel of Persia. If you comment on all three, you’ll get entered three times. (Look at all those correctly used commas! I’m cured!)

Now for Roseanna’s wisdom:
Ready for your next dousing in the grammar pool? I sure hope so, because Grammar Girl (oh, we’re friendly now—you can call me GG) is ready to really dive in!
One of the trickiest things to master is—you guessed it—the comma. I am a comma nazi, and I admit it. It’s all courtesy of my AP English teacher, who would dock you half a letter grade for each mistake in your essays, including a forgotten or extra comma. This a huge issue, so it gets its very own post.
There is some gray area in comma placement, but there are some general rules.
Lists—most sources agree that in a list of items, you should include a final comma before the “and.”
Compound sentences—when a sentence is comprised of two (or more) independent clauses (as in, if you separate them from the sentence, they would be a sentence on their own), you need a comma before the conjunction. BUT—if it’s a sentence with one independent and one dependent clause joined by a conjunction, no comma. Examples:
YES TO COMMA: I know it, but I can’t do it.
NO TO COMMA: I know it but can’t do it.
Do you see why, there? Because the “I” makes the phrase in the first example a complete sentence on its own, an independent clause. But leaving out the “I” in the second means it can’t stand on its own, so it’s dependent. And since it’s dependent, it gets no comma.
Appositives—remember these? Those phrases you could remove from the sentence without changing the meaning of the sentence? Yeah, those—they need to be set off in commas. Example: Clara, the youngest child, knew her place.
Introductory dependent clauses—these are those phrases that start with “when,” “as,” etc. They get a comma after them if the phrase is five or more words (gray area, LOL), but not if it’s fewer. So: When talking grammar one must listen well. BUT: When talking about the intricacies of grammar, one must listen well.
In quotations—I often see mistakes when one has to decide between a comma and a period at the end of a line of dialogue, before the narrative resumes. Here’s the rule. If you follow the quote with a tag (“Hello,” she said.) then it gets a comma. If you follow the quote with an independent sentence, what we call a beat, then it gets a period. (“Hello.” She tucked her hair behind her ear.)
These are your general rules. They get complicated when you get into specifics, but in general, don’t sweat them. That’s what editors are for. 😉 So long as you’ve got the basic rules down, you’ll be fine.
Have questions about them? A particular example you’d like me to look at? Well, bring on the comma llama questions!