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Above is one of the elusive and rare creatures we sometimes call a comma. Many of the people I've critiqued for don't seem to know very much about the comma. That's a problem.
Let's start.
Now, depending on the manual of style that you happen to be using (and yes, there's a thing called a manual of style. It clearly shows what and how you should write and punctuate certain sentences and words. Crazy, I know), then you might be using commas in a variety of ways.
Some rules though, are always in vigor.
If you want the common reader to take you seriously then the very least you can do is to write using proper punctuation. In this part we're going to focus on commas, since the poor things are the most abused of the punctuation tools.
I'm warning you all now, I won't go over every rule and this isn't a concise or definitive explanation of the comma. I will, on the other hand, link you to sites that can help you fill the gaps, as it were.
There are two things that decide whether or not you will (or won't) use a comma. Rules and guidelines. The first are musts. The second are sorta/maybe optional. Perhaps it's because of that difference that so many can't figure it out. Or maybe the people on this site are just stupider than I had realized. Peu importe.
Subject and Verb
Those two things are the most important parts of your sentence. The "what" and the 'what's happening to it." Don't put a comma between the two. Ever.
Wrong
You, wrote something.
Right
You shouldn't write, ever.
Lists
Use commas to separate the items in a list. Whether or not you place one after the "and" is up to you. I like Oxford commas, but don't always use them.
Wrong
I picked up a pony your mom some ammo and a pizza on the way home.
Right
Guys are smarter than girls because we have muscles, deeper voices, and hairier armpits.
Comma-Junction
Use a comma to connect a conjunction (FANBOYS For, And, Nor, But, Or, Yet, So) to the main body of a sentence. This isn't one of the harder rules. Remember, it goes before the conjunction, not after. Some lines don't need this.
Wrong
I wrote a guide and, it was awesome.
Right
I wrote a guide, and it was awesome.
Also Right
I wrote a guide and it was awesome.
Commas to Frame Information
By that, I mean placing a common on either side of an unnecessary piece of information in the centre of a sentence.
Wrong
You tried to use commas you really did but you failed.
Right
If you pay attention, not that it's hard to be distracted, you might learn a little.
Separating Adjectives
Sometimes, we describe things by lumping a bunch of descriptive words together. Always place a comma between those adjectives. One trick to remember this is to use the word "and". If and fits, then you can replace it with a comma.
Wrong
Wow, that Edgar guy is an ugly mean bastard.
Right
Wow, that Edgar fellow is a cool, collected young gentleman. His junk must be huge.
And that's all I'm going to cover today because this is getting boring. I know it's not the deepest of guides, but it should serve as a refresher for some. The rest of you, those that never paid attention to commas before, ought to follow the links below. You'll learn a thing or two, and it's a good reason for me to not beat you senseless later.
Keep warm, stay cool.
http://grammar.ccc.commnet.edu/grammar/commas.htm
http://www.quickanddirtytips.com/education/grammar/where-do-i-use-commas
http://en.wikipedia.org/wiki/Comma