Some familiarity with the Circle of Fifths (Google it) is helpful in understanding how E and A play in the key of C. A song like All the Things You Are can provide a helpful walk through of how this works. But even if you know all of this theory and more, I agree that making it sound right in YOUR musical context is more important.

DC Ron
BiaB Audiophile
Presonus Studio One
StudioCat DAW dual screen
Presonus Faderport 16
Too many guitars (is that a thing?)