Well providing you actually want to be one, here's the advice I would give:
Get the hair right. It's like what emo girls are known for I guess.
Your buzzwords are fringe, hairdye, volume.
Next step, clothing.
Stripes and polka dots are pretty big, stuff with skulls on it, tight jeans, skater gear, black mixed in with brightly coloured... There's no real rules as such, but somewhere between goth, punk and Japanese cartoon characters is where it's at.
As you can see above, accessories are pretty important. Probably even more important than the clothing. Big sunglasses are in, bands and bracelets, costume jewellery will do fine - nothing too expensive. I guess you could say they look almost cheap or trashy (sorry, not sorry).
Make up is required.
Emo makeup tip #1: Use eyeliner
Emo makeup tip #2: I mean a lot of eyeliner
Stick to thick foundation, the paler you can go the better pretty much.
Brightly coloured eyeshadow is not a bad idea.
Tattoos and piercings?
Also, when it comes to taking photos of your emo look - filters are you friend, and don't be afraid of posting selfies. Lots of selfies.