I think it is, first of all, a person who can listen to people constructively, attempting to hear all the aspects of the situation in order to be able to give sound advice. It's also important for this person to be honest, trustworthy and steadfast, guided by wisdom and able to avoid judging 'cause these are necessary conditions for giving good advice. I would also add that in some situations it's really essential for an adviser to be compassionate while in others confident and optimistic.