Depends on the culture. In this answer I will focus on modern French, modern European, and one of a number of American "passes". How and when food is served in which order is as much a function of the season as it is the chef's idea of what to serve when and the diner's decision how to have it presented.
Personally, I have long thought that whatever the particular merits of breakfast, hieratic zeal as the main course was in fact a rather dubious way to start the day. So it is that I welcomed a new study that purportedly was about debunking breakfast, but was really about debunking dogma for breakfast.
I realized that with a plethora of food options across campus, it's important to be able to navigate the dining halls to determine what is best for us physically and mentally. So, here are some of my favorite tips I've gathered from nutrition blogs, friends, my own experiences and, of course, the maternal unit.