I am a first year computer science major. I went to a job fair, handed out resumes, much to my surprise I got an interview and eventually an internship as a developer. I explained to the interviewer (who will be my boss) that I am only a first year and do not have a large amount of experience programming. He simply told me that because I have a strong background in math (I am almost done with my BA in math, plus I have some grad courses under my belt) the he is confident I will do fine. I do well in all programming courses but I still feel that I am at a disadvantage. Right now, I really just want to do good at this job when it starts. The job will be using mostly C#, but besides obviously learning some C#, what is the one skill that you wish you could have learned before you became a real programmer?
Any advice is greatly appreciated, but if you have any books in mind please tell. Thanks!