Don't use don't; use do not.

If you are writing something formal such as an essay for class or a cover letter for a job, avoid using contractions. Here are examples:
don't = do not
isn't = is not
I'm = I am
aren't/ain't (slang) = are not
Let's = let us
haven't = have not
won't = will not
can't = cannot (watch the spelling; it is all one word)
It's = It is
There's = There is/There are
They're = They are
They've = They have
I've = I have
Contractions should be avoided in formal writing. However, don't (do not) confuse contractions with the apostrophes used in possession: Bob's car. Possessive apostrophes are fine in formal writing.

Use your words and not punctuation for emphasis.

There are a few different crutches new writers use to add emphasis in ways that just look silly. These should be avoided if you can use your word choices or the position of your words to create the emphasis.

She told them she would go if she had to. (Using italics to force the reader to read your sentence correctly is rather lame.)

She told them that she would go, but only if she must. (The last word of a sentence has power. Use your word choice, must, and the positioning of it to better create the italics' effect.)

Her boyfriend is the "wrong" sort of guy. (It is sloppy to use quotation marks to add emphasis. The sentence would be fine without them.)

I am very excited to be here!! (Double exclamation marks are overkill; in fact, avoid a single exclamation mark unless you never use them anywhere else on the page. It is so much better to use good words to express yourself.)

I am delighted to be here. Being here is a thrill.

What punctuation do I use with like, such as, and including?

None. How's that for an answer! I'm not quite sure why people feel the need to add a comma, semicolon, or colon around these words. I suppose when we make statements like "He had many bright ideas such as self-cleaning carpet and solar-powered snow melting devices," we do tend to pause a little before or after the "such as" as if waiting for a drum roll. Here are examples of INCORRECT punctuation with like, such as, and including:

X He had many bright ideas such as: self cleaning carpet and solar-powered snow melting devices.
X I bought a ton of groceries; including pet supplies, toiletries, the entire produce section, and yogurt.
X Certain behaviors do not belong in public, like picking at scabs and cleaning fingernails.

With the first example you might be thinking of the use of a colon if the list is introduced by a complete sentence: "He came up with two of the most innovative ideas ever: self cleaning carpet and solar-powered snow melting devices." In that case you can read the sentence before the colon and it makes sense: "He came up with two of the most innovative ideas ever." But if you read the "sentence" before the colon with the such as, it would not make sense: "He had many bright ideas such as." Kind of leaves you hanging doesn't it?

Does the punctuation go inside or outside the quotation marks?

The answer to this question depends on what punctuation we're talking about. The little guys (commas and periods) go inside the quotation marks. The big fellows (semi-colons and colons) go outside the quotation marks. At least, that is the general rule. But if you have in-text citation involved at the end of a quote, you kick the period outside the quote and place it after the in-text citation parentheses. Here are a few examples:

A survey of local Dads reported that "nine out of ten will overprotect their daughters" (Brown 23).
Not surprisingly, last Friday night my dad said, "You have to be home by eleven."
"I don't want to come home that early," I replied.
He was worried that I was going out with "the wrong sort of fellow," but I trusted Jason completely.
Dad told me, "I am going to wait up"; however, the lights were out when I got home.
I kidded Dad the next morning that he was "one out of ten": He was the type of dad who would rather get some sleep than keep track of his teenager.

When quoting, where do I put the punctuation?

Oh, this is a tough one. In general, semi-colons and colons go outside the quotation marks while periods and commas go inside the quotation marks. However, when it comes to the final period in a quotation, where you put it completely depends on the situation. If you are quoting from a source for your research paper, you will kick the period outside the quote and after the in-text citation like so:

The study shows, "Over 50% of new writers worry about punctuation" (Prill 37).

(Note: I am completely making up this statistic and source. Don't quote me on that!)

If you are writing a personal reflection piece and happen to quote a family member's famous words at Aunt Betty's wedding, you will not cite a source and the period will stay inside the quotes like so:

At his sister's wedding, my dad shocked the family by announcing "I object to Betty marrying this good-for-nothing couch potato."

Semi-colons in a long, laborious list

There's another, less frequent use of the semi-colon that can really come in handy when you need it. If your sentence has a long list that involves commas not just to separate red, white, and blue but also to separate parts within each listed item, then you need semi-colons between the items. OK, that explanation probably didn't make sense. Here's an example:

Before the sale could be complete, the house had numerous problems to fix such as no gutters, downspouts, or drainage tiles; leaky faucets and rusted iron pipes; rotten, termite infested floor joists; and a roof with the old shake shingles, two more shingle layers over the top, and multiple patches of tar on the weak spots.

The list of items wrong with the house begins after the words "such as" and includes four items, as if I had said the flag was red, white, blue, and green. However, the first and fourth items have within them three separate parts requiring commas and the second item has two adjectives requiring a comma (that's another post I should make), so if I had put commas where I put semi-colons we would have a mess of commas! The semi-colons are big enough to show us where the four items are, and the little commas show us the parts within each item. This situation shouldn't come up often in your writing because sentences like this are drudgery to read.

Semicolons are tricky; they can be lovely or awful.

The main use of a semicolon is to separate two complete sentences when the second sentence adds more information to the first. The sentences should have a close relationship, like in the title of this post. If I had written "Semicolons are tricky; my favorite punctuation is the colon" these sentences are not related closely enough to warrant using a semicolon. Thus, the semicolon here is a cop-out, just stuck in between because the writer didn't know what else to do or wanted to show off and did it poorly. Examples of good semicolon usage are as follows:
Amy couldn't wait for the weekend; she desperately needed to chill out after working so hard.
The dinner party was a complete disaster; no one felt well after eating the turducken.

Semicolons use this same pattern when two sentences are combined with words like however, moreover, therefore, consequently, and for example.
The house was close to foreclosure; however, a relative paid off the mortgage at the last minute.
Doctors have sloppy handwriting; consequently, their written prescriptions are hard to decipher.

For another use of the semicolon that is less common, see my post on punctuating long lists.

What is the difference between a colon and a semi-colon?

I get this question a lot. People tend to confuse the two. First, a colon is this : while this ; is a semi-colon. If you think about the two as emoticons, the colon is straight forward looking at you, while the semi-colon is winking. Second, each has specific uses. Let's start with the colon. It is used after a complete sentence when what follows is either a list or a definition. For examples, see my post on the colon. The semi-colon is used most often between two complete sentences when the second sentence adds more information to the first. It has a poetic power when applied correctly, but it looks silly when misused. For examples, see my posts on semi-colons and on run-ons (under Option 2). Also semi-colons can be used to separate the items in a list -- instead of using commas -- if individual items in the list already contain commas. Otherwise, the overwhelming amount of commas would befuddle the meaning of the sentence.

Should I use a colon here?

A colon is used in two ways: to start a laundry list or to start a definition. As a laundry list, it comes at the end of sentence and is followed by a series of things. For example, "Jerry went to the grocery to get everything he needed for the big game: chips, beer, burgers, cola, and wine coolers for the ladies." (Jerry is a good ole boy.) The colon takes the place of saying including or such as. A common mistake people make is to put a colon after the words such as or including. That's unnecessary and considered wrong. So if you have written the sentence "Jerry picked up a lot of groceries including chips, beer, and burgers" don't insert a colon after including. The colon also can be used after one sentence and before the next one if that next one somehow defines the first one. For example, "John came very close to the truth: He was due for a lay off, but not because of poor performance." You won't see this use of the colon very often, because it demands a direct relationship between the two sentences that is very clear and powerful. Most often, you will see two sentences that are closely related but have a softer connection, where the second sentence adds more information to the first. That's when you need a semi-colon.