It's or Its

"It's" is contraction of "it is" or "it has".
Examples:

• It's (It is) a plane!
• It's (It is) my bed time.
• It's (It has) been a long time.
• It's (It has) been good to know you.
• It's (It has) got to happen soon.

"Its" is possessive form of it (belonging to it).
Examples:

• The bird lost some of its feathers.
• Where is its head office?

Most of them is or are?

Question: "Most of them is.." or "Most of them are..."
Answer: "Most of them are..." is correct.
Explanation: Though "most of" is singular, but "most of them" refers to several persons or things, therefore it is plural, thus "Most of them are..." is correct!

"You and I" or "You and me"?

Question: "You and I" or "You and me"?
Answer: Both are correct.

The two personal pronouns, "I" and "me" are often used wrongly!

"I" is used along with other subjective pronouns (we, he, she, you and they) when pronoun is subject of the verb.
Examples:

• You and I are going to gym. ("I" is subject of the verb)

"Me" is used along with other objective pronouns (us, him, her, you and them) when pronoun is object of the verb / preposition.
Examples:

• He blamed you and me. ("me" is object of the verb)
• He is going to gym with you and me. ("me" is object of the preposition)

"Excited" or "Exciting"

Question: "I am excited" or "I am exciting"?
Answer: Both are correct.

Excited is an adjective that describes when someone feels happy and enthusiastic about something.
Example:

• I am excited. (something makes me excited)
• She was so excited that she couldn't sleep.

Exciting is an adjective that means something is making you excited.
Example:

• I am exciting. (I make other excited)
• The book is so exciting.

"take lunch", "have lunch" or "eat lunch"

Question: Do I say "I take lunch", "I have lunch" or "I eat lunch"?
Answer: "I have lunch" and "I eat lunch" are correct. "I take lunch" is wrong.

When you are talking about meals, you should use "has/have/had" or "eat/ate/eaten".

Examples:

• I am going to eat dinner.
• Have you had breakfast?
• I am having a meal.
• I have a lunch date.
• What to eat for lunch today?
• Stop talking while you are eating a meal!
  

References:

• http://www.usingenglish.com/forum/ask-teacher/126205-eat-lunch-have-lunch.html
• http://www.englishforums.com/English/HaveALunchAndHaveLunch/cjdbc/post.htm
• http://www.goodenglish.org.sg/improve/commonly-mixed-up-words/i-take-breakfast-or-i-have-breakfast