Mistakes made with the English pronouns I and me have been increasing exponentially for years. The difference is actually very simple – let me explain it to you.
I is the first person singular subject pronoun, which means that it refers to the person performing the action of a verb.
I want to go.
This is the one I like.
You and I need to get ready.
Tom and I are going to the movies.
Me is an object pronoun, which means that it refers to the person that the action of a verb is being done to, or to whom a preposition refers.
David told me to leave.
He gave me ten dollars.
Between you and me, this is a bad idea.
She needs to talk to Joe or me.
The Bottom Line
This confusion usually occurs when you have I/me connected to another pronoun or name with "and" or "or." I believe that the confusion begins when someone says something like "John and me are ready" and that is corrected to "John and I are ready." The speaker then thinks, "Oh, the word ‘and’ means that I should always use I." This is not the case. "And" has nothing to do with it; the reason you say "John and I" in that sentence is that "John and I" are the subject. If they were the object, you’d use me: "He told John and me to get ready."
If you are not good with grammar concepts like subject and objects, there is still a very easy way to decide whether to use I or me: try out the sentence with just I or me (or if you need a plural, we or us – "we" is equivalent to "I" and "us" is equivalent to "me."):
He told Tom and (I or me?) to get ready.
He told I to get ready? NO
He told me to get ready? YES
Therefore, He told Tom and me to get ready.
If John and (I or me?) get married, we’ll have two kids.
If me get married? NO
If I get married? YES
Therefore, If John and I get married, we’ll have two kids.
Just between you and (I or me?), this is a bad idea.
Because "between" needs to be followed by a plural, we’ll use "we" and "us" to figure this out.
Just between we? NO
Just between us? YES
Just between you and me, this is a bad idea.
And whatever you do, please don’t use a subject pronoun and object pronoun together!
He and I – correct: "He and I are going to town."
Him and me – correct: "She told him and me the truth."
Him and I – WRONG
He and me – WRONG