Advice
It is strange advice but I think it was one of my favorite parts of my internship. Whenever somebody in the firm or in your particular internship asks you to go to lunch, always say yes. I found this is where I learned the most about the people I was working with because we weren't talking about accounting or clients. We would talk about almost everything, career advice, hobbies and interests, current sporting events, what you did over the weekend; it just helped me connect with everyone in the office a lot more.