Teaching ESL is the best job ever!
Since ESL students are trying to take in a lot at the same time, structure helps them acquire the new language easier.
Take into account the age of your student when choosing your curriculum. For middle school and high school there are innumerable sources with simple vocabulary but high interest.
There are materials designed for college students too; some deal with grammar and some with pronunciation.
Plan ahead, fill in gaps, and try to anticipate what the student teacher's direction is in order to prepare the student for material to be taught.