Have a passion for what you want to do and things that interest you and do them to their fullest.
Get experience but don't fake it. They'll know when you're faking.
I've built most of my college experience around working with athletes with my Sports Medicine program and dedication through triathlon.
I've had my government internships, surgery observation hours, etc, but that won't be what I focus on when I'm in an interview. Everyone has that.
Not everyone can say they took one thing and went all out for it. For me thats Ironman... find what it is for you.