Economics is a subject that is very difficult to cram for unless you have amazing memory. It requires constant revision and you have to make sure you stay on top of the new material you learn every lesson. If you let it pile on top of you, there will be way too much info to cover for the exam.
What I do is read the textbook and make notes of the content ahead so when we go through it in class and I am more familiar with it. Economics is an easy subject to learn ahead, nothing should really challenge you, since most of the content is very straightforward.
Hope that helps!