To add to the excellent response above, I would add empathy. Remember Atticus's mantra - to crawl inside someone else's skin before judging them. Atticus consistently does this in all instances - it is why he has Jem read to Mrs. Dubose, it is why he does not get angry with Mr Ewell when he spits in his face, it is why he puts up with his sister's digs at his parenting skills and his decision to defend Tom, it is why he makes the deal with Scout so they can still read so her first grade teacher doesn't get angry at her. In doing this, Atticus always leads by example and follows through with his actions.
Another trait is that Atticus is honest. I think the best example of this when he believes Jem was responsible for Ewell's death. Atticus doesn't hesitate to begin planning the trial and what will happen. However, it is Tate who finally gets Atticus to believe that Jem did not do it.