Well, by my groups standards, "Emo" people, music, and clothing are all "Goth" rejects. It tends to gravitate towards the more high-end commercial products though.
For my school, "Goth" kids (whom i hung out with), wore black clothes (that they may have dyed themselves), baggy chain pants, and had black hair. But their clothes were often torn and home repaired, mostly with duct tape. Even the chains were poorly attached. You could often find them listening to Metal.
Where as the "Emo" kids (whom i did no hang out with) bought their clothes ripped, black, and with chains attached (Extremely well made). Their hair was black, but often with highlights of any color they pleased (red, green, white. Didnt matter really). And the music they listened to tended to be less "Metal", and more, "Kiss my love who left me for another man" depressing.
I guess in the end, it mostly comes down to the:
1: Music
2: Clothing
3: Hair
This was my experience in middle/high school several years ago at least.