For you, dear Plimco, I will try to address the comma rule. I must say, though, that this is difficult for me because I love commas. I throw them in whenever I think two clauses need a tiny break between them.
That, I think, is the comma’s main job–to give your eye a chance to rest before scurrying down the rest of the sentence.
So, you can use a comma between clauses: I saw Mrs. Mustard in the library with a candlestick, but I was too afraid to scream.
You can use a pair of commas to set off part of a sentence that’s less important than the rest.
Say Don Coyote burst into the room, yelling, “Which way did that girl go with my tamales?”
We could say, “Don Coyote, the girl, who was wearing blue shoes, went that way.” and it would be fine to set “who was wearing blue shoes” off with commas, because that’s just added information. He’ll still be able to find the girl whether or not she has blue shoes on.
But say that Exador burst into the room and said, “Did you see that stripper who ran off with all my money?” and say that we’d actually seen two women in g-strings come through, each with a load of cash.
Then we would say, “The girl who was wearing the gold g-string is upstairs.” See, if we take out the clause “who was wearing the gold g-string,” Exador loses vital information that would let him discern which woman he should chase.
You can also use commas to separate items in a series. I went on a walk, had some breakfast, and typed on the computer.
But you must never use a comma to break up two complete thoughts.
Let’s use this example:
I cannot leave. I’m having your baby.
Right now, with a period separating them, they seem like two very distinct thoughts. I cannot leave. Also, I am having your baby.
But say that I want you to get that I cannot leave you because I’m having your baby. I may feel that the period is too strong a break between them, that those two clauses need to be joined by something softer, more delicate.
I cannot leave, I’m having your baby.
No, for sentences whose meanings are more closely linked than could be implied by a period and yet are too independent for a comma (note that, in order to make the sentence above correct, I could add a conjunction of some sort–but, and, if, therefore, etc.), I must reach for that rarest of punctuation mark: the semicolon.
I cannot leave; I’m having your baby.
Tada! Oh, semicolon, I love you. Have my babies. No, wait, I’ll have yours. Depending on the font size, I should be able to squirt out your kids no problem.