'One may tolerate a world of demons for the sake of an angel.'

Now that we've assessed what a good leader is like[1], time to go wider. A good person. What is a good person like, how would he/she act?

There are plenty of people who don't appear to be very noble or 'good', but are told to have hearts of gold. People who don't act as good as they are, for one reason or other. Sometimes due to peer pressure, sometimes due to necessity, sometimes because they really are pricks. But the most objective way of determining whether a person is 'good' or not is by observing the actions. After all, it is the actions that we can observe, so far we have not been able to peek into the soul of a person.
While it is difficult to define 'good' actions, some generalizations can be made. For instance, a 'good' person would not willingly betray someone's trust if there is an option not to and not cause a more negative effect by the act of non-betrayal. In essence, he/she will choose the action presenting in the least harm coming to the fewest people.

"The happy life is thought to be one of excellence; now an excellent life requires exertion, and does not consist in amusement. If Eudaimonia, or happiness, is activity in accordance with excellence, it is reasonable that it should be in accordance with the highest excellence; and this will be that of the best thing in us." - Aristotle

Now that is a difficult guideline to follow. Situations that befall us are rarely so black and white. Just look at the Doctor: there is a man with a choice, either let a single planet of his own kind perish or spell doom for the whole Universe. On a mathematical scale it is no choice at all, one life for billions. On a personal scale, it is trading all he knows, everyone like him, his home, his life, for people he knows nothing about. We were told that was the choice he had to make, yet it is not the choice that was described afterwards. Now we know the choice was not whether to save a few and sacrifice the many or to save many and sacrifice the few. It was whether or not to use a planet full of life as bait to lure yet another civilization to near extinction. It is not a choice that is easily made. If he chose not to, his planet would still have died. Then again, would a 'good' man kill millions of beings for doing what they believe in just because he fancies it?

But of course fiction is riddled with ethical dilemmas, it is what makes it so addictive and educative. But that is not to say ethical problems are smaller in real life. Take doctors for example. They have the responsibility of manipu... er... convincing people that what doctors deem to be best thing to do is actually factually the best possible thing to do. Even if the people do not accept that as the truth. Sure, belief in the medical system is a huge part of getting better, but often patients (and/or their relatives) are put in front of a choice where there is only a single accepted answer. And not just in the case of pulling the plug on braindead patients or harv.... er... donating their organs. Though you might think 'surely when a person makes a decision that's it, surely a decision is a decision', but that is only true if it is the decision the doctors want, otherwise it is only a temporary setback. While it may not appear ethical at first sight (that's why they don't call it 'manipulating' when it so clearly is), it serves a greater goal. That goal being gaining more resources to help those who would actually benefit from their help, instead of tying them up for people who have no practical use for the resources or ever will. Helping more people surely must be ethical, right?

"You cannot have a greater ideal with the smaller ones being compromised."

If a good person aims to be good, to be excellent, then his actions cannot in any step conflict with his beliefs. Then again, often if he refuses those actions, the consequences are even worse in regards to his beliefs. As Sheppard Book used to say: "If you can't do something smart, do something right.". Beyond that it's a crapshoot.