When a personal pronoun is used as a direct object, an indirect object, or the object of a preposition, it must be in the objective case (me, us, you, him, her, it, them).
Exercises:
Pronoun case (such as I vs. me) 1
Pronoun case (such as I vs. me) 2
Pronoun case (such as I vs. me) 3
Pronoun case: review 1
Pronoun case: review 2
Related topic:
Subjects and objects of infinitives