Thanks for asking! We have a whole handout on that. The main idea is this:
Build a good foundation in math, physics, and chemistry (C or better).
It takes a long time to get to junior classes in chemical engineering, and yet it is only really in those junior classes that you will use much of the preparation that you are building. In the fall junior classes we use: calc 1, calc 2, calc 3****, differential equations, physics 1, and freshman chemistry. Thus, it is important to build a good foundation.
Another good tool to look at as you plan your college experience is the prerequisite map. The interdependence of the chemical engineering courses with the foundation courses is clear from the course prerequisites for the chemical engineering classes.