The most important thing is to learn how to not get phazed- they will expect you to learn a lot very quickly, and you need to be sure that you stay focused and do not get overwhelmed. You will make mistakes. Possibly bad ones. You will deal with unkind customers. You need to learn how to make sure that does not rattle you. After that, a strong work ethic and the ability to learn quickly will make you one of the best technicians in no time at all. The good techs are the ones who go out of their way to learn new skills. Also, do what you can to make customers happy- at the end of the day you work in customer service.