When to I or me?

Use "I" when it is the subject of a sentence, meaning you are the one performing the action (e.g., "I went to the store"). Use "me" when it is the object of a verb or preposition, meaning the action is being done to you (e.g., "She gave the book to me"). A helpful tip is to remove other subjects or objects to see if "I" or "me" fits correctly in the sentence.