Know the subject well: When you start learning a subject, get an overview of the subject by looking at the syllabus and contents.
Try to grasp all the concepts of chemical engineering: Whichever subject you are going to learn, first make a glossary of concepts that you would be learning.
Get your hands dirty by trying out various things using the labs in your institute or through simulations: Chemical engineering is all about practical applications and not only theoretical knowledge. Whichever concept you are learning, just try applying it practically in your daily life or by simulating it.
Start studying mathematical subjects first: Mathematical subjects take time to learn, as you have to apply your prior mathematical knowledge in your domain. It is not just plain solving of mathematical sums, so you need to understand how to apply both mathematical and chemical knowledge. Subjects like Process Calculations, Heat and Mass Transfer, Fluid Mechanics, etc., are mathematical, so they need to be taken first.