Rule 1
You may end a sentence with a preposition. Just do not use extra prepositions when the meaning is clear without them.
Correct:
That is something I cannot agree with.
That is something with which I cannot agree.
Correct:
Where did he go?
Incorrect:
Where did he go to?
Correct:
Where did you get this?
Incorrect:
Where did you get this at?
Correct:
I will go later.
Incorrect:
I will go later on.
Correct:
Take your shoes off the bed.
Incorrect:
Take your shoes off of the bed.
Correct:
You may look out the window.
Incorrect:
You may look out of the window.
Correct:
Cut it into small pieces.
Incorrect:
Cut it up into small pieces.
Rule 2
Use on with expressions that indicate the time of an occurrence.
Examples:
He was born on December 23.
We will arrive on the fourth.
Rule 3
Of should never be used in place of have.
Correct:
I should have done it.
Incorrect:
I should of done it.
Rule 4
Between refers to two. Among is used for three or more.
Examples:
Divide the candy between the two of you.
Divide the candy among the three of you.
Rule 5
The word like may be used as a preposition and in informal writing, as a conjunction. In formal writing, use as, as if, or as though rather than like as the conjunction.
Examples:
Prepositional usage
You look so much like your mother.
Conjunction usage
You look like you are angry.
OR
You look as if you are angry.