Everyone puts down the grammatical issues inherent in writing as the last concern when in fact they are so important like the semi-colon in the classic line: It was the best of times; it was the worst of times. Or was that the other way around? I don't care to see the semi-colon misued and abused as in having it replace the simple comma where a comma will do, but on such as that Dickens' line, let the semi-colon rip. The semi-colon is merely the comma screaming out to its cousin the period to join it because "I can't do this job alone! I was not constructed to stop the full weight of a freight train of an entire sentence--a whole thought! The comma rather prefers to travel with fragments and lists, and items you find in a list. It travels with whole sentences only when combined with some stronger element. Either the period (it's cuz or a conjunction -- and or but so, etc). Then an only then can the "lowly" sign of the comma be used to hold off the object of one sentence (thought) from the subject of a trailing sentence (thought). Without the full coupling of the conjunction with the comma, we are into run on territory.
If the period is the basic mark to end a sentence or thought, then how do we add noise to that period? We exploded it out via the exclamation point. Add a sense of questioning or inquiry and the period is topped not with a straight up exploding mark but a squiggly, queston mark. When we use two periods, one atop the other as in the full colon, this is calling in the muscle for sure. We use full colons in the event of setting up information to be displayed or listed the other side of that double-dipped period as in the following: bird cages, boxes, full and empty, used aquariums, scattered bird seed, and hampster shavings.
Or in any list found in a pet store after the fire.
Quotation marks tell us who said what to whom when and where IF we keep each speaker in his own space by giving each person in the dialouge his or her own paragraph indent. It becomes a jumble of confusion when two and three speakers are jammed into a single paragraph, no matter how fat the paragraph. Treat dialogue like the comic strip artists do; give each speaker his own "balloon". Only difference is the prose balloon is represented by the quotation marks. We writers can learn a huge amount from how artists depict conversation in their comic strips. Makes for a great exercise to rewrite a comic strip, not changing the words but embellishing the narrative around the speaking parts, giving each speaker his and her own space (indents and paragraphing), and have the storyline come off as still funny or entertaining or enlightening as the comic "genius" had planned but WITHOUT the visuals. This requires using the same dialogue for the joke to work, but it also means the author must weave in the telling asides in narrative. It points up the fact that you needn't ever use "he said" or "she said" if you instead attach an action/narrative line that "belongs" to this speaker in the same space as his speaking part.
Instead of saying: Mike leand in and said, "I want you to come clean with it now." It could as well be done as: Mike lit a cigarette, leaned across the table, and glared at Jonas. "I want you to come clean with it now."
The first example is a "how he spoke" line. The second example is a "how he acted" line. One uses the comma, the other the period.
These lowly marks have a place, and we owe a debt to the monks or whoever it was that organized all this for us eons ago. Our job as authors is to get the grammar right, and trust me, if you have a contnual bad habit or habits in this area, editors will not read beyond the page. E.B. White's Elements of Style is of great help here, of course, but trust me, any ordinary grammar book, like the tried and true Little Brown Book ought to be looked at from time to time, just to remind ourselves of the wonderful knowledge of language we discovered in fouth and fifth grade, to revisit this area. Revisit sentence types, sentence combining, active vs. passive voice, and any book by Langan on the subject of grammar is required reading for those who have as yet to master the grammatical basics.
Have fun with it, and if it is a mystery (everyone should write a mystery) have Gun with it,