When I was young, I had the habit of writing something and then grabbing a handfull of commas and throwing them in. I'm still not a master of punctuation, but I am getting better at it. Here are a few rules to mesmerize:
1.) Remeber those co-ordinating conjunctions? (and, but are the most commonly used)I remember them by dressing them up in outfits and standing them at intersections (I'm a visual learner). Well, put a comma after them when they are directing two independant clauses.
2.) A comma can be used to set off a clause of a phrase that simply adds information.
The girl, red hat strategically placed on her head, rode her horse down the road.
It sure beats: The girl gode her horse down the road.
3.) Another method of comma use that's fun is when you want to mess with people's heads. Everybody has used; When, After, Before, Because, If, Although...in the second part of a sentence marked by a comma:
Example: The rescue crew launched their boats, after the monstrous waves calmed down.
Reversing this for effect.
Example: After the monstrous waves clamed down, the rescue crew launched their boats.
Use it at the begining or end of a paragraph, but don't use it too often or you'll just irritate people.
4.) This is a good one. It lets you take your character somewhere quickly. In this commas are used in a series.
John ran down the hill, onto the dock, and dove into the water in an clumsy attempt to drown himself.
By using commas in a series you can really move things along.
5.) The last one I'm going to mention is helpful in creating a disjointing feeling:
Sometimes people write: The calm and placid lake reflected a perfect image of the boat.
Commas inserted to ser off a phrase out of its natural order.
Example: The lake, calm and placid, reflected a perfect image of the boat.
I like the second one, it just feels artsy.
So, I hope you find the following rules helpful.