I think a few of the most valuable lessons I learned being a waitress were:
1. Treat everyone the same.
2. People are in bad moods when they're hungry. Once they have food, they're much nicer.
3. Many people don't like certain foods. Mostly it seems it's onions, tomatoes, olives and broccoli.
Oh! - mushrooms. Lesson: Everyone is different. No use getting upset about it.
4. Not much in this world is about me.