Welcome to an overview of grammar in the English language. Take heed and avoid further embarrassment because the Grammar Nazis are angered.

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Apostrophes

Apostrophes are used for two reasons:

1) to show possession of

2) to indicate a contraction

1) This writer's bad grammar appals me. (This is because the bad grammar belongs to the writer)

2) That's their bad grammar. (This is their bad grammar - take out the "i" of is and put in an apostrophe and make it one word.)

It

A small but very important word. This is an exception to the above rule.

"It's" means "it is" - for example: "It's a tiger!" is the same as "It is a tiger!"
(This can also apply to has - eg. "It's rained." or "It has rained.")

However, to express possession you do not use and apostrophe. Apostrophes only express contractions with "it."
To express possession you merely write: "Its tiger had a green nose."

"Lie"

As few of you have realised the word "lie" and the word "lay" are different words. Although this is understandable as it is rather complex. To understand this explanation you need a brief grounding in verbs. Verbs have 3 main parts - The present tense, the infinitive form and the perfect tense. There is some confusion over these words as "lie" also has more than one meaning and there is a degree of confusion between the two separate words as they look similar at times. Firstly we will clarify the both definitions of "lie" and then the definition of "lay."

Lie:

1) to be in or move into a (usually) horizontal position

2) to tell untruths

Lay:

1) to put something into (usually) a flat or horizontal position with some degree of care

Now the differences:

The first definition of lie conjugates like this:
I lie, to lie, I lay

The second:
I lie, to lie, I lied

"Lay" conjugates like this:
I lay, to lay, I laid

As you can see there is a lot of crossovers with the words. Here are some examples to help you grasp the differences.

Lie (def.1)

(present) I lie back on my bed after having read some fanfiction with a good plot line and impeccable grammar.
(infinitive) He was about to lie back and go to sleep when he remembered the fanfiction alert he had received earlier that day.
(perfect) The tiger lay in the grass last Tuesday.

Here are some more secondary parts of the verb you may find it useful to know:
(future) I will lie down and go to sleep when I have read and reviewed this fanfiction, which, by the way, has impeccable grammar.
(imperfect) I was lying on the floor when I spotted a missing apostrophe.
(pluperfect) I had lain undisturbed until the Grammar Nazis arrived.

Lie (def.2)

(present) I often lie about how many reviews I got.
(infinitive) I know it is wrong to lie about homework, but I really had to update my fanfiction.
(perfect) I lied about the ending of Harry Potter; Dobby dies.

Here are some more secondary parts of the verb you may find it useful to know:
(future)Iam twelve years old, but will lie about my age so that I can have a fanfiction dot net account.
(imperfect) I was lying to the tiger.
(pluperfect) I had lied to the teacher about my score on the last apostrophe test.

See how few differences there are in the pattern? It is vital that you get the perfects and pluperfects correct or else the Grammar Nazis will be angered.

Lay

(present) I lay my laptop in my desk when I have finished fanficing each evening.
(infinitive) I am careful to lay my coffee far away from my laptop as I do not want to spill it onto the keyboard.
(perfect) I laid the baby tiger in the crib.

Here are some more secondary parts of the verb you may find it useful to know:
(future)I will lay the homework on your desk first thing tomorrow - or maybe the day after. I need to finish my fanfiction update tonight.
(imperfect) I have been laying the tigers in neat lines, but they keep frolicking.
(pluperfect) I had lain the papers on his desk but the tiger had eaten them by the time we got back.

Numb3rs

The age old question: "Should I write it in words or figures?"

Well comrades the answer is simple:

numbers one - one hundred are written as one, two, three, four, sixty-seven, twenty-eight, ninety-three, one hundred (in words.)

numbers 101+ are written as 101, 102, 103, 167 452, 142 458, 10 000 010 101 (in figures)

On the note of writing in figures; the universally recognised way of signalling each thousand is to use a space - like this: 1 000 (see the space?) This - 1,000 - is in correct. It is how the older generation in Britain and many other places tend to do it. Kick the habit. Now.

Conjunctions and Commas

The two Cs. Communism and Capitalism... wait no. Wrong website.

If you use a short conjunction (such as: and, but, for, nor, yet, or, so) feel free to use a comma. However, this must ONLY be before the conjunction. A comma after the conjunction is incorrect. Although in natural speech we sometimes pause after a conjunction: "The tiger was eyeing them hungrily - they should have been scared, but..." if you want to create this pause your best bet is using the ellipsis. A comma is wrong. Learn this.

You're and Your

You're is a contraction of "you are."
You're in love with that tiger.

Your is possessive.
Your fanfiction has the most impeccable grammar.

There, Their and They're

Really if you don't know this by age thirteen... well where have you been?

They're is much like you're. "They are in love with that tiger" and "They're in love with that tiger."

There is to express a place either concrete or vague.
"Does the tiger like living there?" (vague) "The book is over there - check the spelling of Hermione so I can spell check this fanfic." (concrete.)

Their indicates possession.
"That is their tiger."

Less and Fewer

The simple way to remember this is to remember less is for singulars and fewer is for plurals.

I have less time than I would like to be an angry grammar Nazi on fanfiction.net.

I have fewer mistakes than the other fanfiction writer because I heed the advice of the grammar Nazis.