What can I do during this summer to get into a top internship in the next summer?

I am currently a rising sophomore interested in law, economics, and international relations. I am aware that summer internships and research programs are integral in demonstrating passion for college admissions, and I am planning to apply to some of these internships and research programs for my next summers as a rising junior/senior. What can I do right now that will boost my chances of getting in? I know that the programs are very competitive, so I want to start preparing now. For example, would taking online courses on places like edX help? What should I do?

PS. I am aiming for Ivy-League colleges, so please feel free to provide realistic and demanding advice.