Snowie ,
Firslty, Prepare what you have to teach , such as which pages.
If you have no idea at all, try to download some exercises or work sheet in the internet.
Secondly, look through all what you have to teach.
Thirdly, prepare what kinds of method you are going to teach.
Fouthly, also prepare the homework for them.
Finally, preapre that you have to teach students you have neven seen before. Some of them must be very hard controlled if you are very nice to them.
Hope you received my message before going to the less.