When do I use “I” instead of “me” ?
Always try using "I" or "me" in the singular, for the same sentence. For instance, people might say: "Robert and me are going to town." Which is wrong, because one does not say "Me am going to town." Therefore the correct way to say it is "Robert and I are going to town."
However, this sentence is also wrong: "The police arrested Robert and I", because if it were in the singular, one would not say "the police arrested I", it is, "the police arrested me." Therefore one should say, "The police arrested Robert and me."