Find an emo person and study him/her. If you're not comfortable doing this in person, there are many website devoted to emo culture with photos for reference. Make a note of clothes, hair, makeup and general mood.
Make sure to bring these elements to your artwork. Incorporate hairstyles and facial features common to emo kids, such as black hair that is long in front and covering one of the person's eyes, a sad disposition and generally dark clothing representing a dark mood.
Draw a person in the same way you normally would, and then add the emo characteristics. Make the hair darker and the expression sad. Draw the person looking down or crying. Shade the clothing with hard strokes of the pencil and outline the eyes for a more dramatic effect.