2) According to their tactfulness, mainly. It's also important for me that they can be quiet most of the time. And the positive intention behind their actions. You notice it when people are there to mess with you or if they're gentle souls;
3) Same as point 1. I just like people when they're as described in point 1, and when they reflect those characteristics it's easier to share common activities. Having shared interests or being already forced to share time is a bonus point. It's good when you get along well with colleagues.