Copywrite vs. copyright, or "use the right right, writers!"

"Copywrite" is a rarely-used verb that means "to write copy". Used correctly, you will most commonly see this in noun form as someone's job title: "I am a copywriter." This means that they create the text that goes in an advertisement.
"Copyright" is a noun meaning "the legal authority to create reproductions", or, phrased more obviously, "the right to make copies". (It can also be used as a verb or an adjective, but it still has to do with the right to make copies.)
Just about every time I've seen people use the word "copywrite," they were wrong.
Easy rule: unless you are talking about the process of creating advertisements, use "copyright."

Affect vs. effect, or "Don't Verb That Noun!"

"Affect" is a verb. When you want to make a mark on something, you want to affect it.
"Effect" is a noun. When you want to know whether you've made a mark on something, you want to know what effect you've had.
There is one exception common enough to be worth mentioning for "effect:" when you want to cause something to happen, "effect" can be the correct verb, thus:
"I want to effect a change in the way people write."
Just to be completely honest, there are also cases where "Affect" can be used as a noun. These, however, are very few and far between.
Easy rule: "Affect for Action, Effect for End-result."

Under-apostrophizers, or "Dont abdicate your responsibility"

Okay, I talked about improper use of apostrophes a little bit before. Some people are apparently so scared of using them incorrectly that they don't use them at all, even when they are clearly called for. Unfortunately, leaving the apostrophe out of a contraction very often leaves you with a different word.
I'd is not the same as Id.
I'll is not the same as Ill.
Can't is not the same as Cant.
Won't is not the same as Wont.
If you write "Id like to go, but I cant." then you have just said that one part of your brain desires travel, but you are busy leaning to one side (or possibly speaking in a jargony or sing-song manner). This is probably not what you intended to say.
There's no easy rule for this one, unfortunately; just a plea for writers to put forth the necessary effort to apostrophize correctly.

Ellipsis abuse, or "Not 5, not 12, just 3!"

The ellipsis, used to mark a pause or to indicate that material was elided, is one of the most abused constructs in online writing. I blame this on lazy people relying on the typematic effect of computer keyboards. Back when you had a manual typewriter, you didn't hit that period any more than you had to. Now it's too easy to just hold the key down and let the dots flow: "................................." But that's the WRONG thing to do! An ellipsis consists of EXACTLY THREE PERIODS: "..." No less, no more. The only use for "..................................." is to provide a line across the page in a menu or other tabular listing that you are setting without the benefit of HTML.
Correct usage: "I said no... then I smacked him."
Incorrect usage: "I don't know what to do................................................................Maybe I'll take a nap."
Now, having said that, occasionally you may use an ellipsis at the end of a sentence. If you do that, it IS CORRECT to include a period at the end of the sentence, directly after the ellipsis. While this may APPEAR to be 4 periods in a row, really it is an ellipsis and a period.
Correct usage: "Their voices faded out as they meandered off into the distance...."
Don't be lazy and lean on the period key. You don't know how many periods you'll get that way. Do it right.
Easy Rule: There are 3 periods in any ellipsis. It's just that simple.