Pictographs are used to communicate visually. The imagery should be simple in design but may be complex is thought. Everyone, no matter of the viewers native language or literacy level, should be able to read a pictograph.
You will be creating pictographs for daily activities for the school. Think about your day. What do you do each day that someone who is unfamiliar with this school might not understand. For example, rather than having a typed message on dumping your tray after lunch, you could make a pictograph.
This website is filled with examples from Gerd Arntz, http://www.gerdarntz.org/isotype . I recommend you check it to get ideas. Of course, you may not copy his examples and as always, you need to sketch out ideas first.