This topic has always fascinated me. I just read Plato's Meno where Socrates tries to determine what a virtue is. He came to the conclusion that it is what makes men good. He also came to the conclusion that it must be innate in people.
Benjamin Franklin disagrees with this and felt you could learn virtues by practice. He created a method where he would list all the virtues he wanted to obtain, and the first week he would concentrate on the first virtue on the list. The second week he would focus on the second, while still maintaining the first, and so on. This way it would be not be an overwhelming endeavor.
I found a website with an extensive list of virtues, http://www.virtuescience.com/virtuelist.html. I picked the ones I felt were the most important to me, I'm sure everyone's list would be different.
Patience:
I think this may be the most important virtue and one which I had little of when I was younger but have come farthest in mastering. Lots of things in life like dieting, working out, and saving money don't show immediate results and without patience it's easy to get discouraged and give up. Short term patience is important as well. Getting stuck in a long line can make one irritated which is an unpleasant state to be in. Think of it instead as a good time to relax and think about life. Just sitting and thinking is probably undervalued today amongst many people.
Persistence:
Patience is a prerequisite for persistence. Lots of things in life are hard. When I learned to play guitar I had a lot of trouble with many chords. Especially that pesky F! Now playing the guitar is one of my favorite things to do and all those initial frustrations are just a memory.
Humility:
This one might be the one I need to work on the most. No one likes to be around someone who thinks they wonderful. Even if you feel like you are, some restraint in bragging about it will make you a more appealing person and more enjoyable to be around.
Discipline:
I am working hardest at the moment on this one. Cleaning your house everyday for 20 minutes is a lot easier than 2.5 hours straight once a week. It's a lot easier to wake up and play video games for a few hours in the morning, but waking up and getting everything you want done will make you feel better the rest of the day.
Confidence:
You'll never accomplish anything difficult to do if you don't have confidence. Once you can become great at something which first seemed unattainable you realize you can conquer anything you attempt.
Cleanliness:
No it's not easier to find your stuff when you room is a mess, contrary to many a teenager's belief. Being clean and organized is like changing the oil in your car regularly; it will keep your life running smoothly.
Courtesy:
Practicing courtesy will give you the same benefits as humility.
Curiosity:
You'll miss out on some great things in life without curiosity. Try every food you can, get involved in as many things as you can and read up on every subject that fascinates you.
Frugality:
This doesn't mean being cheap. It means maximizing the way you spend money. You can make a lot better meal at home for $10.00 than you can get at a fast food restaurant and $5.00 spent on a used book will give you more enjoyment $20.00 on a new DVD.
Honesty:
"Oh what a tangled web we weave, when first we practice to deceive!" Sir Walter Scott. You can save yourself a lot of stress in life by being honest.
Moderation:
Lots of things I enjoy in life, wine, gambling, video games can lead to ruin if taken too far.
After writing this I would define a virtue as something which is hard to do but makes life more enjoyable. I disagree with Socrates, virtues can be learned, taught, it should be practiced. I do agree Socrates that it is what makes men good.