If you haven’t already, read my comic “Grammar Guru” before reading this post.
People often have trouble with pronouns when using compound subjects or objects.
Grammar Tip: Compound subjects or objects = “me and frog” “frog and I” etc. If you’re not sure which pronoun is correct (me? I? he? him? etc), simply imagine the subject or object as a single pronoun. You should be able to (at least intuitively) determine which pronoun is correct.
To use Cookie Monster’s examples:
1) “Me and frog love cookies” –> remove “(and) frog” to leave a single pronoun = “me love cookies”. This, obviously, is incorrect; the pronoun “me” should be “I”. Therefore, “Frog and I love cookies” is correct (first person pronouns always come last in compound subjects/objects; this is just how these pronouns collocate. “I and frog” is awkward and descriptively incorrect)
2) “Share a cookie with frog and I” –> remove “(and) frog” to leave a single pronoun = “Share a cookie with I”. This, again, is incorrect; the pronoun “I” should be “me,” and therefore “share a cookie with frog and me” is correct.
Same applies for he/him, she/her, we/us, they/them, etc.