[Eric18]

You might use pictures, magazines, catalogs, and picture dictionaries if they are really low. How large is their vocabulary? That will be the key factor - along with their motivation (passing a standardized exam? getting a good grade? traveling to an English speaking country?).
I've had students create collages to expand vocabulary and share stories. You can also pass out postcards and ask them to write a message, in English, to someone. That helps you assess their language skills, provides a practical application, and should be within reach for high-beginning students. You could also have students create their own flashcards of nouns, verbs, etc. I learned this technique from my co-teacher in a high-beginning adult ESL class. I was sceptical, but her predictions of student engagement were correct. It also allowed the students to choose what 25 words they wanted to learn.
You're facing a large class so this sort of group activity offers a few advantages. Students can work together, help and quiz each other. They will learn by doing...as you circulate around the room offering help and gentle corrections. You might also want to download some of the free worksheets available on this website too.
Will you have class sets? Or will you be copies your materials? That will heavily influence the type of materials used. The school should provide picture dictionaries. Do you have a preferred textbook? If not, you might consider the Side by Side series which is so popular in American adult schools. They also have a huge amount of support material making your life easier. The downside of Side by Side is that it seems a bit juvenile at times, but you're teaching teenagers so they might enjoy the same aspects that used to bother me. Another possibility is the Interchange Series, but they target a slightly older group of students (university). There must be a solid multi-skills, communicative style textbook for EFL high school students, but I don't know its name.
Good luck! Remember the goal is progress, not perfection.