What are some cultural adjustment tips for a friend going to study abroad in the United States?

My friend is going to study abroad in the United States, and they are seeking advice on how to adapt well to American society. They are particularly worried about mistakes that might arise from social and cultural differences. The first piece of advice I gave my friend was to refrain from asking personal questions like age or marital status when meeting someone for the first time. I also informed them that excessive physical contact among men or making noise while eating can be uncomfortable in the U.S. Do you have any other tips or cultural differences to be aware of in American life to help avoid mistakes? I especially need advice regarding restaurants, gyms, and meeting people. I don't intend to criticize cultural differences, so please feel free to share your experiences.