How to handle communication about the class outside of the official channels, when I am a TA for a class that a friend is taking? I am an undergraduate student who was asked to TA this semester for a class that I have wanted to TA for for a while. Duties would likely involve basic grading of exams and projects as well as answering questions during office hours, but no recitations or other classroom teaching. 

However, a close friend of mine will be taking the course with the professor who asked me to TA. The course started this week (TAs will be finalized soon and start within a few weeks) and my friend has already asked me a few basic questions on the topic, which I answered. Additionally, I met with him to assist him with the introductory assignment. It was only after this that I was asked to be a TA. 

I wanted to know how to best conduct myself, both from now until I am officially made a TA as well as after I become a TA with regards to him in this course. Should I simply say that any questions should be saved for my eventual office hours and deny any additional assistance, so as not to give an unfair advantage? If he were to send me a bug (cs course), would it be improper to assist outside of any office hours, even on trivial problems?
It sounds wise to steer your friend towards your office hours, although there's probably no need to insist on this.

However, I would not give additional assistance with debugging beyond what you would do for anyone else.  The most important thing is for your friend to learn how to do his own debugging!

There's one more thing you can do: fill your professor in on the situation before the semester starts.  And then, as the semester unfolds, if any specific dilemma or uncertainty arises, ask the professor for guidance.

That is my offhand take on this.  However, when you speak with the professor, s/he may have more specific guidance.