What do you consider to be "important characteristics?"
I guess what I would say she must have had two very important characteristics -- intelligence and determination. The reason I say this is because she managed to become a pretty important person even though she was a woman in a time and place where it wasn't that easy for women to get ahead.
I also say this because most people don't realize that she wasn't just some tired woman who decided not to change seats on the bus. Parks was already an experienced community activist who was a leader in the civil rights community in Birmingham. In fact, she had (soon before her arrest) spent several weeks at a school for community leaders. The civil rights community had been looking for a good way to attack segregation (there had been two teens that same year who had been arrested for not giving up their seats, but they were seen as bad symbols of the black community) and she decided to provide it herself.
So, to get to that kind of position, she must have been smart and determined and I'd say those were her most important characteristics.