When reading sentences out loud, a writer can hear where punctuation belongs. For example, in the sentence "Although it was raining out they still went for a walk," a reader will naturally pause after "out"; similarly, when a sentence begins with an introductory clause such as "For Christmas" and continues with "we roasted a turkey," a reader naturally pauses after "Christmas." Both of these cases require commas.
Exclamation marks express a strong command or declaration. Adding an exclamation mark to the sentence, "Call the police!", creates a sense of urgency that would not otherwise be there. However, overusing exclamation marks has a counterproductive effect. In the sentences, "Mountain climbing can be dangerous. You must learn correct procedures! You must have the proper equipment! Otherwise, you could die!", the exclamation marks exaggerate the sense of urgency. Dropping all exclamation marks except the last one would be more effective.
Run-on sentences occur when a writer joins two independent clauses without a coordinating conjunction, for example, "The iceberg broke off from the glacier it drifted into the sea." A writer can correct a run-on sentence with different kinds of punctuation. Separate the two clauses into two sentences with a period, introduce a coordinating conjunction preceded by a comma or connect the clauses using a semicolon.
Some writers find semicolons and colons so confusing they avoid them altogether but both can enhance writing. Semicolons and colons do not function similarly. A semicolon joins two independent clauses that a writer does not wish to separate into two sentences, while a colon introduces a list, a quotation or an appositive (a word or phrase that renames something just mentioned). Semicolons can also separate long items in a list following a colon, as follows: "She had four professors from four different countries: Dr. Smith, Ph.D., of Washington, D.C.; Dr. Jones, Ph.D., of Montreal, Canada; Dr. LeBlanc, M.D., of Paris, France; and Dr. Schwartz, Ph.D., of Berlin, Germany."
Apostrophes baffle some writers who can't remember the differences between words such as "its" and "it's" and "there" and "they're." The key is that "it's" and "they're" are contractions of the phrases "it is" and "they are." When writing, pause when you have used an apostrophe and make sure that the contraction makes sense. If a contraction doesn't make sense, as in "I put it over they're [they are]," use the correct synonym, "there."