Writer's Workshop #1: Basic Sentence Structure

Hello, visitors, and welcome to this, the first in a series of posts I'm going to call "Writer's Workshop." (I was going to go with Atelier de Perfectionnement, but I had trouble spelling it.) This will be a series of crash courses on English grammar, spelling, and narrative. I may be a proof-reader, but my job is much more difficult if you don't know these basics. As such, rather than teach all of you separately, I'm going to make these posts for you! Everypony who comes for my help should read these first. Better to have the basics fixed before I go in for the hard stuff.
Anyway, here's the first one: Punctuation.

Usually, sentences end in a period.
I am going to the store.
You can also use question marks or exclamation points, appropriately.
Do you like my hat? Of course I do!
(I'm sure you know this already. Review is important!)
Quotations are when it get hard. When a quote starts the sentence, it usually ends in a comma, not a period.
"Take me to your leader," said the alien.
If it ends a sentence, you use a period.
I said, "Take me home."
The part "said the alien" or "I said" is called a dialogue tag. Sometimes, the dialogue tag is in the center. Here's what you do for that: If the first part of the quote is a complete sentence, the dialogue tag ends in a period.
"Drive us closer," said the commissar. "I want to hit them with my sword!"
However, if the first part isn't a complete sentence, the dialogue tag ends in a comma.
"As I was saying," my teacher continued, "all molecules have mass."
This makes a lot of sense when you think about it. Periods end sentences, but commas merely pause them temporarily. Thus, you always use commas with quotes if the sentence keeps going.

They'll probably be longer than this as I make more. Now you'll never end a sentence incorrectly again! :)