If you find it confusing whether or not you need a comma before “and,” the answer is that usually you do.
If “and” separates two short words or phrases, you can skip the comma:
A flowered quilt and odd-shaped pillows were strewn across the sofa.
Usually, though, “and” separates matters of greater complexity:
Put the wagon in the garage, and don’t forget to pick up your toys.
A comma is appropriate in that second example, because it separates two larger ideas, which might be confusing and blur together if the comma weren’t there.
How about using a comma before “and” in a series? Surprisingly, either of the following is correct:
tall, dark and handsome
tall, dark, and handsome
Using a comma before “and” in a series is optional. I always use it, because I’m a book editor. In the book publishing industry, which follows The Chicago Manual of Style, we do place a comma after the second item in a series. In the newspaper industry, though, which abides by the AP Stylebook, the comma is left out after the second item in a series.
AP style: tall, dark and handsome
CMS style: tall, dark, and handsome
If you’re neither an author nor a newspaper journalist, you can do it either way, as long as you are consistent. (Authors, see my article ‘The Chicago Manual of Style: What Authors Need to Know.)
Jessi Rita Hoffman … book editing by an industry professional