You are unlikely to go wrong if you take ECON 101 (Principles of Microeconomics) as soon as you can - preferably during your first semester. ECON 101 will also provide you insight into the economic thinking behind major topics such as inflation, discrimination in labor markets, pollution, and barriers to free trade. Your understanding of world events will be enhanced, and you will be a better citizen because of it.
It is also a pre-requisite for all other economics courses except the First-Year Seminar, ECON 150. Several interdisciplinary majors require an upper-level economics course or two, and before you can take those, you must have credit for at least ECON 101. Most upper-level courses have both ECON 101 and ECON 102 (Principles of Macroeconomics) as prerequisites.
If you plan on majoring in economics, you should complete ECON 101 and 102 in your first year. Before you can declare your economics major, you need to have credit for at least one semester of Calculus (MATH 108, 111, or 131). If you don't have AP or transfer credit for Calculus, consider taking that your first year as well.