As someone who has taught economics to many students over the years, I have two main tips. One of them is fairly generic and applies equally to economics and to any other class. The other is more specific to economics.
The generic tip is to work hard and study. This is, of course, applicable to any class, but that does not make it any less true. My students who have read the book and come to class with questions have typically done better than those who try to get by simply by listening in class and cramming when it comes time for a test.
The less generic tip is to work on your ability to think logically. More than most social sciences, economics relies on logical thought. There are only a few rules and definitions that must be learned in basic economics. Once you master those, you are being asked over and over to think logically and to apply the rules and definitions that you have learned to situations from real life. Many students of mine have struggled because they can memorize the rules and definitions but cannot think logically in a way that allows them to figure out which rules apply to various situations from real life.