Subject & Object

It and you can be subject or object but
-- I, s/he, we and they are subjects.
-- while me, him, her, us and them are objects.

Object pronouns are used after a preposition.
Tim is working with me today.

Subject pronouns are used after as and then if they're followed by a verb.
I am taller than he is.

When not followed by a verb, the object is used.
I am taller than him.
I am taller than he. (Formal)

When the subject or object is two words joined by and, you need to check your pronouns carefully.
Tim and I are working for Jack.
Jack employs Tim and me.

Never use them instead of those when in front of a noun.
Give me those keys.

Whom & Whose

Whom can stand for a person only if the person is the object of the clause.

Whose stands for someone to whom something belongs.
The man whose hat blew off.

After a preposition, use whom instead of who and which instead of that.

Nouns 1 | Nouns 2