[Azzid]

Neat tut that i found useful and I wanted to share with you all. So here it is.

To vs. Too vs. Two: "To" refers to a certain destination, whether it's physical or metaphorical. "Too" implies that something is an addition, or it's present in excess. Obviously, "two" is just a number.
"I'm going to the party tonight."
"Don't get too smashed, alright?"
"Two is a number." (I got really creative with this one).

Its vs. It's: While this one can easily be a result of a simple typo or your phone's autocorrect thinking it's smarter than you, there is still a wealth of people that can't differentiate these two. "Its" is possessive and "it's" is a contraction of "it is."
"It's a very nice day outside!"
"Put the camera on its tripod."
An easy way to figure out whether your form is correct is to read your sentence aloud with "it is" replacing "its/it's." If the sentence doesn't make sense, you are employing the wrong form.

There vs. Their vs. They're: I like to think the distinction between these words is pretty obvious, but I see people interchanging these three words all the time. "There" refers to a certain place or destination that is being referenced. "Their" is possessive and can be applied to singular or plural nouns (if it's applied to a singular noun, the object being referenced is almost certainly third person). "They're" is a contraction of "They are."
"Put the desk over there."
"The property is theirs."
"They're not going to be at school today."

Your vs. You're: "Your" implies the possession of an object, while "you're" is a contraction of "you are."
"That backpack is yours."
"You're not going to practice today, are you?"
If you forget the distinction, just read your sentence aloud replacing your form with "you are." If it doesn't make sense, you screwed up.

Then vs. Than: I see this one far more than I feel I should. "Then" is an adverb that is used to set an event in a certain time, while "than" is used for comparisons of objects.
"We are going to school, and then we are going to your place."
"My grammar is better than yours."

Effect vs. Affect: Here's a wordy distinction: "Effect" is a concluding result of an affecting agent, while "affect" is something that produces some certain reaction. "Effect" is a noun, and "affect" is a verb.
"Will the solar flare leave any lasting effects?"
"That movie really affected me."


Good vs. Well: "Good" is an adjective that refers to the quality of something that's already done, but this doesn't apply to questions that start with "How." If the question asked starts with "how," then you're going to answer with "well" and not "good." When describing the being of the self, you will say you're doing "well," not "good."
"He did a good job on that test."
"I think I did well on that test."
If you "do good," that means you're performing good deeds, and not simply feeling well.

Who vs. Whom: This one is pretty common, and I can usually forgive misuse of this one. "Who" is a nominative pronoun and is used when it's the subject of a sentence. "Whom" is an accusative pronoun and is used when placing the indirect/direct object of a sentence.
"Who is going to the ball game tonight?"
"You're going to the dance with whom?"
An easy way to remember this is the placement of the pronoun in the sentence. If it's not in the first few words of the sentence, chances are you're going to be using "whom."

Me vs. I: "Me" is a pronoun that refers to a certain action being done to the accusative party. "I" is a pronoun that refers to the agent performing the action. This one is usually misused when an "and" or "or" is thrown into the mix. Here's an example:
"Michael and I are going swimming."
This correct, because if you took Michael from the sentence, the sentence would me reduced to "I am swimming." Still makes sense. Now, let's try that again, but replace "I" with "me."
"Michael and me are going swimming." - This is very wrong.
Since you have applied an accusative pronoun into a nominative position, the sentence no longer makes any sense. If you pulled Michael from the sentence again, you get "Me am going swimming."
If the sentence makes sense without the other subject, you have correctly constructed your sentence.

Could've, Would've, and Should've: These contractions can be separated in a way that is phonetical to the speaker. This form is almost always "Could of," "Would of," or "Should of," and that is incorrect. These three contractions end in the word "have," not "of." Just think of the way the contraction is spelled, which should give away its proper separation.
"I could of ordered a pizza tonight." - This is wrong.
"I could have ordered a pizza tonight." - This is correct.

Use of commas: Commas are always used to separate one grouping of words from another. They are usually used in the production of lists, lengthy sentences, or introductions to letters.
"I think my grammar sucks, but that's just my opinion."
"For example, I've surely made a grammar mistake within this post, and that makes me a hypocrite."
Regarding the production of lists, there's this thing called an "Oxford comma," which is just putting a comma before the last item on the list. As far as I know, this is optional and depends on your way of speaking/writing.
This thread will surely be helpful to you if you need more information.

Insure vs. Ensure: This one is also kind of tricky, but only if you don't know the definitions to these words. "Insure" pretty much only applies to insurance, since its definition refers to protection against a possible contingency. "Ensure" means to make someone certain of something.
"I crashed my car, but I forgot to insure it."
"Ensure you buy car insurance, or you'll get screwed."

Compliment vs. Complement: To compliment someone is to give them praise, but to complement someone is to easily fit together with them. "Complement" usually refers to two pieces fitting together very well or enhancing the effect of one another.
"Thank you for the compliment, it made my day!"
"I think we complement each other very well."

Less vs. Fewer: "Less" refers to objects or ideas that can't be properly quantified, while "fewer" refers to things you can count.
"My ability to construct smooth sentences is less than my ability to play Call of Duty."
"I bought fewer than ten items at the grocery store."

Lay vs. Lie: "Lay" is a transitive verb that requires a subject in order to be used, while "lie" is intransitive. The past tense of "lie" is "lay," and people become confused when this distinction needs to be applied. "I lay on the bed right now" is incorrect. "I lay on the bed last night," however, is correct.

Use of semicolons: Semicolons are used to separate two sentences that are closely related but should remain in the same thought. They should not be confused with colons, which introduce a new thought within the same sentence.
"Come to school early tomorrow; I have a surprise for you."

Disinterested vs. Uninterested: "Disinterested" implies a neutral stance. Although Google tells you that "disinterested" can mean uninterested, this is incorrect. "Disinterested" means someone is unbiased. "Uninterested" means exactly what it sounds like it means.
"The referee was disinterested in the winner of the game."
"The bored girl was uninterested in her brother's soccer game."

[Jebusfathead]

Don't really need this, but it's is not a 'contradiction' of it is, like that grammar sucked whoever made that.

[Skryptec]

Very good one,

The only thing I have problems with is well and good.