What sort of person lives a good life? An excellent person, a person of excellence. But then what does excellence mean? Since it is excellence as a person, we're talking about a quality of character.
Changing the center of discussion to talking about a good life in terms of the excellence of persons is an important move. Many things that happen in lives are accidental; not everything about them is within our sphere of influence. In matters of character however, of seeking correct views and developing adequate feelings about what's going on around you, of choosing carefully and aiming to do the right thing, it's always clear who is responsible: you are. Thus, although it doesn't add anything specific yet, the change of perspective from looking at what makes a life good (the entry point of ethical discussion) to asking what sort of person would lead a good life marks some progress already. Of course, this is still only the beginning of the journey, since now we've our work cut out in saying more specifically what it means to be excellent.
The term 'excellence', for one thing, can mean different things. One of its typical senses is that of being outstanding, being better at something, or more of something, than others. This sense implies a comparison with someone else; it's not what I mean by excellence. (It's not a helpful notion, for it makes excellence something that depends on external circumstance: you might be a bad person indeed, but live among a group of much worse ones, and in abominable circumstances — does that make you an excellent person? In that common sense, it would seem so. But not in the sense which I use; one wouldn't be excellent if one were just simply the smallest evildoer within sight.) And if it is not a notion based on a comparison, then we can't explain it in terms of degree either, for that would require some quantitative scale, some unit in which to measure.
It's often easier to recognize failure to be excellent than to detect excellence itself. (Candidates for excellent behavior may still turn out to fall short of actual excellence for many reasons, although it didn't show at first sight, whereas apparent non-excellence is rarely re-interpretable as being in fact excellent.) Worse, however, than failing to be excellent in a particular situation, is not even accepting that excellence is what we should go for (if we want to lead a good life). Not managing to achieve it, in a given instance, does at worst mean that you have to try harder next time, that you're not yet where you want to be (which, in all probability, will be the case most of the time). Not even aiming at it, on the other hand, indicates you're seriously misdirected, and with time you won't get closer, but you'll drift away from your most important goal (that of leading a good life, and spending your time wisely).
Such misdirection can show itself in many different ways. It may lead you towards greed in one of its myriads of forms: going for pleasure and convenience, splendor and luxury, power and wealth, fame and celebrity — any one of those false aims (or a combination of them) which have no measure built into them, which will drive you into wanting more and more, which will get stale under your hands even before your enjoyment of them ends, which will leave you with nothing of real substance after you have thrown a lot of precious life time after them; it may have you pushed around by fears and weaknesses: cherishing foolish hopes and illusions, giving in to nebulous anxieties and unsubstantiated fears, indulging in pointless lamentations and uncontrolled flare-ups, favoring aimless industriousness and taking the line of least resistance whenever there's a chance of getting through with it — all of them currents that will take you into regions where they get stronger and stronger, draining away your strength and freedom little by little every time you go along with them. The only way to lead a good life is to resist them always; in effect, that is what it means to become excellent. It may not work in many instances, but unless you make it your primary goal, the cases in which you fail and end up drifting in the wrong direction will outweigh those in which you do the right thing, form correct views and respond with adequate feelings. Unless you make a constant and determined effort to move in the direction of living a good life, unless, that is, you aim to become excellent, you will lose this struggle. It's an upstream swim: you can't hand yourself over to the current, let things drift just as they want, and still reach your destination. Take care.