How do you form relationships with your professors?

I’ll be applying to grad school next school year, and my future program puts a large emphasis on reference letters. I’ve always been able to form good relationships with my professors in smaller classes, but all my current and future classes are 50–100 students, so how do I go about forming a good rapport with them so when I ask for references they actually know who I am?

if it matters i’ll be applying to speech pathology or audiology programs