I can't help it. I teach English grammar, and comma faults disturb me even when I overlook them. In English, the general rules are as follows:
Do not use a comma before the coordinating conjunction when joining compound elements in a sentence (subjects, verbs, objects, prepositional phrases, etc.), except when the compound elements are independent clauses. Thus, Lynn's first example, "Clark ran his fingers through Lois's hair, and whispered sweet nothings in her ear," would be correctly written without the comma since it is compounding verbs: Clark ran ... and whispered. The lack of comma tells us that both actions were done by the same subject.
In the case of compound independent clauses, the comma alerts the reader to the fact that one clause is completed and what follows the coordinating conjunction (for, and, nor, but, or, yet, so) is part of a new clause, and therefore a new sentence idea rather than a piece of the old one. That's what Lynn's next two examples are: "Lois gasped with surprise and she giggled when his beard stubble scratched her cheek" and "Clark slipped his arm around her waist and she closed her eyes in anticipation." Both sentences should have a comma before the "and," although some publishers or employers will accept the lack of a comma since each independent clause is relatively short. However, I teach my students the more restrictive grammar rules because they are correct no matter who the reader is.
Lynn's last example was a complex sentence, which contains a dependent and an independent clause. When the dependent clause starts the sentence, it is separated from the independent clause by a comma because there is no other cue word to indicate that the first clause has finished and another begun. Thus, the example sentence should read, "After he kissed her, Lois's eyes popped open in recognition. Superman!" with the comma after "her" to let the reader know that the first clause is finished. However, when the sentence starts with the independent clause, a comma is not necessary since the subordinating conjunction or relative pronoun that begins the dependent clause provides the cue to the reader that the initial clause is finished and another is beginning. Lynn included an example of that in her compound-complex example: "Lois gasped with surprise, and she giggled when his beard stubble scratched her cheek." Notice that there is no comma in front of "when" since the subordinating conjunction itself tells the reader that a new clause is starting.
Wendy is absolutely correct about the use of commas with restrictive and non-restrictive phrases, especially with the problem of only using one comma on a non-restrictive phrase. However, her example is incorrect. In American English, we don't set off prepositional phrases with commas, no matter how non-restrictive they are, and so: "The book with the blue spine lay open on the table." OTOH, I would use commas to say, "The English book, which has a blue spine, lay open on the table."
The most important thing to remember about commas is that they separate sentence elements, not join them. Since I read so many sentences from my students with major mechanical and grammatical errors, I overlook lots of minor comma faults. But I still hate reading sentences with commas in places that separate important sentence elements that belong together or sentences with nothing but a comma between the independent clauses (comma splices, a kind of run-on: Sister Zoe would encourage her class, Miss Fletcher would discourage her class).
