One Sunday each month my mom cooks dinner for a group from church. The group could range from 20-40 + people. She's been doing this for 9 years or more and has it down to a science. It's pretty amazing to witness. I've learned a lot from watching her: what types of food are good for large groups, what are crowd pleasers, how to host, how to clean up as you go, and how to present food nicely.
I think it's helpful to take mental notes at parties you attend of what makes it successful or unsuccessful and why. It'll make you a better host I think.
A couple desserts made for this particular evening. Strawberry rhubarb crisp and brown sugar cookies (forgot to sift the powdered sugar!!)