I vs Me

Whenever you do the action in a sentence (you are the subject,) use "I."

• I saw my dancing teacher in the bus today.

Whenever you have an action being done to you in a sentence (you are the object,) use "me."

• My dancing teacher saw me in the bus today.

When you add a second person to this sentence, nothing should change.

• Mary and I saw my dancing teacher in the bus today.
• My dancing teacher saw Mary and me in the bus today.