Seek out upper division economics courses which require a research paper. Often graduate schools will request a writing sample as part of the application process. Evidence that you can write well and conduct economic research will enhance your chances of being accepted. Before your senior year begin making a list of graduate programs that you may interest you. Contact the advisor for each program and ask for a program description and an application.
Graduate schools require scores on a specified standardized exam.
Look at the appropriate test preparation books - most libraries have copies. Grad school applications will require several letters of recommendations from your undergraduate professors. We can write better letters if we know you better. So don't be shy, talk to us.