Use I as a subject, as in I offered a muffin. Use me as an object, as in Nina offered me a muffin or Nina saved one for me. The same pronoun case applies when another person is mentioned alongside you.
Remove the other person to test it
- Jonah and I brought muffins. With Jonah removed, I brought muffins still works.
- Nina gave Jonah and me a plate. With Jonah removed, the sentence becomes Nina gave me a plate.
- Nina saved two muffins for Jonah and me. The shorter version is Nina saved two muffins for me.
Check the role in the sentence
Look at what the pronoun is doing. In Nina gave me a plate, me is the indirect object. In for me, it is the object of the preposition. The same principle helps with who vs. whom.
