Suggestions for optimizing IIS

We have a couple of public apps that, while they work outside of our network, sometimes perform pretty slowly on different networks. They can take upward of 30 seconds to load.

 

The sites are minimalist, so there shouldn't be too much data being transferred from our server to the client. I'm wondering if anyone has any general advice for optimizing IIS and their web server to make public apps perform as fast as possible?