I have one thought. It is that you should identify an excellent, well-organized student and ask that person to help you with the class. You might as well be frank with the class that you need a student assistant, since you are not familiar with the class and/or the subject matter. If a lesson has to be reviewed, ask the student to help you with it. If a textbook is involved, ask the student to take the class through the steps found in the textbook.
Home page for substitute teachers is located at http://www.teacherneedhelp.com/students/subtch.htm
Home page for classroom teachers is located at http://www.teacherneedhelp.com/students/
Navigate to Home Page "A Packet for Substitute Teachers" - http://www.teacherneedhelp.com/students/subtch.htm