Graduate programs in economics generally care most about quantitative and analytical aptitude. Many graduate schools offer a summer preparation program for a month or so before classes start in the fall. The content is usually a review of relevant mathematics. If your graduate school offers such a program, you are well-advised to take it even if you have a strong math background, because the mathematics actually needed for economics may not have been emphasized in your undergraduate courses. The Summer Training Program offers courses in applied economics and quantitative analysis, plus stimulating weekly seminars.
Tuition is free and a stipend is included.
If you are considering graduate school, please feel free to discuss your plans with me and other members of the economics faculty at Drake University.