What is it? Basically, it’s being "efficient, organized, neat, and systematic":

Conscientiousness is the state of being thorough, careful, or vigilant; it implies a desire to do a task well. 

Conscientiousness is also one trait of the five-factor model of personality, and is manifested in characteristic behaviors such as being efficient, organized, neat, and systematic. It includes such elements as self-discipline, carefulness, thoroughness, self-organization, deliberation (the tendency to think carefully before acting), and need for achievement.

Yeah, that sounds like a trait we all respect. What’s amazing is just how predictive it is of so many things we all desire.

It's a shame we do not encounter this trait in more people.

Can conscientiousness be learned? That is a very good question.

Eric Barker's article seems to think so.