Have patience and quick learner will be one of the kay plus as said be polite to everyone.Being an sys admin is a basically a thank-less job and you have to accept that. When everything going well(you made it possible by spending day and night to solve other peoples owes),nobody turns to you and say "hello",but the moment something goes wrong you might heard that the telephone is ringing too frequently and you have to give lot of unncessary answer to lot of people.
So be prepared for that.I am not scaring you to saying all those ..just try to give you a "Black and White' picture of real life scenario of most sys admins,whether they confess it or not.I have been in corporate for long time and managed corporate infrastructure for different corporates and those are they situation i have come across during those time.
Cheers!