Emo that's closer to traditional punk tends to use strummed open, barre and three-note power chords with really bright clean tones and crunchy overdrive, whereas screamo and metalcore usually involves diads and palm-muted single notes, with both muddy clean sounds and heavy distortion. If you're looking for guidance, I'd suggest listening to the half-decent emo groups like Thrice, Boys' Night Out and Coheed and Cambria, not the derivative corporate stuff like Simple Plan, Lostprophets, Taking Back Sunday, he Used etc. *shudder*