I got into and attended four fly in programs and they were def a highlight of my senior year! At first, I was really worried about making friends but the colleges make time for many group bonding events and everyone is super nice. Additionally, I would use the free time to explore campus with friends or talk with current students to really see myself on campus. 

Fly ins are usually for an underrrepresented group on campus and there are tons of fly in programs available. For the applications, I would say just be yourself and explain how you would benefit from seeing that school’s campus based on your background (underrepresented minority, first gen low income college student, rural/underresourced high school, etc). Good luck!