I have mentioned the Big 5 personality traits before, and the biggest of them all is Conscientiousness. Conscientiousness, or C, is a measure of one's ability to buckle down and work hard, especially at unpleasant tasks. It is correlated with job performance and doing well in school. It is partly heritable, and relatively stable over time. That doesn't mean that C doesn't change over time, rather, it means that relative rankings of C stay the same over time. One unsurprising result of the research on C is that C increases over time. Basically, as one gets older, it is easier to defer gratification and take the long view. However, people who were more conscientious to begin with will still be more conscientious than their similarly aged peers 20 years later.
The five traits of the OCEAN model emerged from research into personality. Researchers analyzed personality questionnaires using factor analysis, and discovered that the answers tended to fall into five groups. These five groups were named Openness to Experience, Conscientiousness, Extraversion, Agreeableness, and Neuroticism. I like the OCEAN model better than scales like the Myers-Briggs, because each trait has real contraries. Either you are introverted, or extroverted, or somewhere in between. The MBTI's sixteen types don't seem all that well distinguished to me. This is perhaps due to the remove from the Jungian theory that spawned it, but it is often hard to tell which type really applies to a given person.
If you are curious where you rank on the OCEAN model, you can take an online test that is part of the research of Dr. Samuel Gosling. I have linked my results below. I especially like the part about a messy desk!