I would try to write an outline of a speech first, and start with writing down some key points that you want to cover. For striving for excellence, I suggest discussing something along the lines of career and future aspirations that can inspire others to be motivated and passionate as they continue their education. Try to be relatable, humble, and open, but be assertive. Think about what would help you be motivated, and then apply that to a larger group of people. I hope this helps!