Hey, this is easy. Parentheses are used to create an aside to the reader, and are less of a break than dashes, but more profound than the break created by a comma or commas. And, unlike commas or dashes, parentheses only come in pairs. Though the decision whether or not to use parentheses can be a judgement call, with practice you begin to see which of those marks—commas, parentheses, or dashes—is most correct. There are basically three different ways to punctuate with parentheses.
Let’s take the easiest use first, which is an independent clause inside a pair of parentheses, by which I mean a full sentence that is by itself inside parentheses but not inside another sentence. (Put another way, this “full sentence” offers ancillary information—an aside, if you will, to your reader—that is not part of another sentence.) Material inside parentheses in stand-alone information must be a full sentence.
Okay, that was my example, the full sentence inside parentheses. Note that the first sentence has its own period, and then the second sentence, the parenthetical sentence that follows 1) starts with a capital letter, and 2) the period is inside the second parenthesis. These are two separate sentences. Do you see it?
Let’s look at the second example, which happens when the parenthetical information (which may or may not be a complete sentence) is part of another sentence.
Again, that’s my example (using a dependent clause, i.e., not a full sentence). Here the parenthetical information is completely inside another sentence. You kick off that information with a lowercase letter and no punctuation inside the second parenthesis.
So this example is incorrect:
How do you WP? (where do you work, listen to music, require a cup of coffee?)
Why? Because these aren’t two separate sentences. This information should look like this:
How do you WP (where do you work, listen to music, require a cup of coffee)?
Do you see how I removed the first question mark and then took the second one outside the second parenthesis? Now we have one full sentence with proper punctuation.
This next would also be correct, because I just made the parenthetical information a full sentence:
How do you WP? (For example, where do you work, listen to music, or require a cup of coffee?)
And here’s my third example, which happens when the parenthetical information comes at the end of the main sentence:
Again, that’s my example (using a dependent clause, i.e., not a full sentence).
The rule is that your dependent clause starts with a lowercase letter and your end punctuation is the period for the main clause, and that is placed outside the parenthesis. The interior punctuation of the parenthetical information (if there is any) just sits there, just like you want it.
Stay tuned for the less common, but still important, punctuation issues that come up using parentheses.