Princess Leia Organa possessed a lot of character traits that helped define who she was as a leader, a warrior, and a diplomat trying to unite a galaxy under the yolk of Imperial tyranny. These traits were ingrained at a young age, and stuck with her throughout most of her life, well into her final years.
A few of these traits disappeared as she mellowed with age, while others only grew in strength, making her a far more capable leader. She was certainly a heroine for the ages, and without the elements that made her who she was, it's doubtful she would have been able to help free the Star Wars galaxy from Emperor Palpatine's clutches.
Her Impatience
Perhaps due to her upbringing, or the fact that she spent so much time organizing and assisting the Rebellion, Leia was prone to impatience. This was especially true if she was dealing with outsiders who were not privy to how things ran inside her own operation.
Those who couldn't keep up were left behind, and she had little patience for those who couldn't adapt, fight, or hold the line. For her, efficiency was a matter of literal life and death, which left no room for errors or shenanigans. Han Solo got the brunt of Leia's impatience during innumerable occasions, but it helped him gain an insight into her personality.
Her Temper
Leia's temper was fiery and legendary, despite her status as a diplomat. Leia was the real hero of the original trilogy, going toe-to-toe with Darth Vader, and standing defiant to the end, which was no small feat. If she had a problem with someone, it didn't take long for her temper to let it out of the bag. And those who crossed her tended to regret it.
Lando Calrissian learned this the hard way after betraying Han Solo to the Empire. After he freed Leia and company, she allowed Chewbacca to choke him out of spite, only to begrudgingly relent when he formed a quick plan to try and save Solo. This was characteristic of Leia, and something her enemies came to fear.
Her Diplomatic Nature
No one rises through the ranks of the Rebellion, while simultaneously playing nice as a government official without some serious diplomacy skills. As a representative of Alderaan, Leia had the ear of many, and used it to influence them to join the Rebellion against the Empire.
On the flip side, she kept up her profile as a Senate official alongside her father Bail Organa, a man who knew full well how the Empire had come to power, and the lives it snuffed out. Leia could broker deals, calm tensions, and form bonds between allies in order to unite against a common foe.
She Completed Her Tasks
Leia was not a person who started things never to finish them. Her duties to the Rebellion were all or nothing, and she wasn't about to stop, no matter how hard the going got. The destruction of the first Death Star gave the Rebellion a major shot in the arm, but the wrath of the Empire took its toll in the aftermath.
Yet, Leia never lost sight of the goal - to cripple the Empire, and free the galaxy. Simultaneously, she helped devise a plan to free Han Solo from Jabba the Hutt's clutches, before resuming her campaign in service of the Rebellion. Leia was certainly not a quitter.
Her Discipline
Leia was disciplined in many things, from diplomacy, to combat. She was even a fantastic pilot, though not quite as good as other pilots in the Star Wars galaxy. That was a big part of her personality, and it forged her like steel for the battles yet to come. Her campaign against the Empire required her to be strong at all times, which was a trait she kept close when the First Order rose to fill the power vacuum.
Even under extreme duress, Leia never lost her cool. She successfully resisted Darth Vader's mind probes, and refused to give up any information about the Rebellion, and she bided her time as Jabba's slave, in order to effect a rescue plan on Tatooine. When the chips were down, Leia waited for the moment to turn things around, rather than come apart at the seams.
She Was Humble
For all her bravado and gusto, Leia was a remarkably humble person. She wasn't at all interested in the trappings of luxury and status that came with someone of her position within the Senate, and she never demanded special treatment as a high ranking member of the Rebellion.
Leia knew that they were all in the same fight together, and that meant avoiding anything that might have fed her own ego. She may have come from royal Naboo blood, but she showed no signs of wanting to be treated any better than anyone else, which is why so many were keen to follow her.
She Was A Strategist
Leia knew that fights with the Empire could turn sour at a moment's notice, and even the best laid plans could go pear-shaped. Therefore, she knew how to strategize in order to effect a win. When conditions on the battlefield changed, she was able to figure out an alternative plan to achieve her desired outcome.
It was this ability to strategize that allowed her to throw a monkey wrench into Imperial plans on a routine basis. Hiding the Death Star plans in R2-D2 was a stroke of genius that single-handedly saved the galaxy from permanent Imperial oppression. Similarly, her strategic mind helped rescue Han Solo from Jabba the Hutt, whom she strangled to death shortly before escaping with a handful of sail barge survivors.
Her Adaptability
Leia's most noteworthy display of adaptability occurred in the original Star Wars film, when she took charge of her own rescue operation to save everyone's lives. If not for her quick thinking and courage, the Imperials would have trapped them on the detention level, putting a quick end to their escape.
This kind of quick thinking and adaptability was one of Leia's strongest traits. She didn't know everything there was to know, but she would evaluate each situation accordingly, and try to adapt in real time. Even under extreme stress, she always kept her eye on the objective, and improvised to reach it.
Her Bravery
Never one to back down from a fight, Leia was the antithesis of a shrinking violet. Indeed, she'd leap headfirst into battle if it meant winning the day. She had no problem jumping onto the back of a speeder bike in one of her most badass Leia Organa moments in order to prevent Imperial scout troopers from reporting the Rebels' location on Endor, and it nearly cost her her life.
Throughout the Star Wars films, Leia showed remarkable bravery in the face of certain death. Sure, she had quite a lot of help along the way, but she was never content to duck for cover. Rather, she'd be the first to pick up a blaster, and jump into the fray.
Her Combat Prowess
Despite her diminutive size, Leia was a force to be reckoned with in battle. She had plenty of experience firing blasters, and by the time she'd grown into young adulthood, she'd seen her fair share of battles. She even went up against legions of stormtroopers with nothing but a blaster in her hand, and no backup.
Leia was a great shot, which made her very effective in battle. Later, she'd learn the ways of the Force via her brother Luke Skywalker, but that only complimented her existing skill set. She knew how to handle herself in a fight, whether it was a ground assault, or a dogfight through the emptiness of space.