It’s hard to tell you exactly what ECs they like to see but it would go along the lines of club/leadership, community involvement, productive summers (research, internships), winning competitions/distinctions for pursuits, and that ‘wow’ factor like starting a non-profit, business, etc. As of now they’re not too strong - they’re a little scattered and lacking some breadth. I would check the results thread to give you a better idea of a strong candidate.