When I say 'balancing a character' in context of a novel, I mean making a character with strengths and weaknesses that will facilitate an ongoing tension. A character needs both strengths and flaws-- even the simplest of characters requires some kind of balance between these two aspects. The most powerful of characters still has a flaw; the slimiest of monsters still has something that makes them admirable.
I actually want to point to Ender's Game and Ender's Shadow as a good example of what happens when you strip a character of this internal tension. Bonzo Madrid is introduced in Ender's Game as being handsome and charismatic. He's a middling Commander, but in a school of geniuses where only so many kids can be promoted, this still puts him in the upper echelon of the students. He is prideful, which causes him to view Ender's dissent within his army as a personal slight and eventually drives him to a homicidal rage when Ender defeats him handily in the Battle Room multiple times (the last time being a humiliation he cannot abide by). But his pride also means that when he confronts Ender in the showers with intent o hurt him, he agrees to a fight on even terms-- leading his henchman at the door, stripping naked as Ender himself already is. He is an antagonist, but Ender still expresses some amount of admiration (and pity) for him; when he first joins Salamander Army he even thinks to himself, "This is a Commander I would follow into battle." We don't like Bonzo, but we understand him.
Hop over to Ender's Shadow, and when Bean meets Bonzo he's clearly already read Ender's Game, because he instantly decides that Bonzo is dumb, not worth his time, and must have only been promoted to show other kids how to function under an incompetent Commander. Every time he encounter Bonzo, Bonzo is nothing but an incompetent bully, and Bean easily outpaces and outsmarts him every time, even being the one responsible for Bonzo trying to murder Ender in the bathrooms. In Shadow, Bonzo is a bully, flat and simple, a profoundly uninteresting. An argument could be made that this because Bean's perspective limits out exposure to Bonzo, and Bean himself is marked as being kind of bad with people (until it turns out he's actually just as good with people as Ender is).
If you read Shadow without reading Game, I doubt Bonzo would register as much of a character at all, because he's just some jackass in the background who Ender kills in an offscreen fight. This isn't just because he's Ender's enemy rather than Bean's (Bean actually earns his ire as well), but because Bonzo is lacking that tension that he had with Ender-- somebody who Ender wanted to look up to, who could have been a good Commander if he had let go of his pride, and whose downfall consequently feels earned but tragic. In Shadow, it's just... well I guess that happened.
When you're building a character, you want to build this tension into them-- strengths and weaknesses alike. This is a fairly well-trod piece of advice, but I find that it's a fairly common issue that, when people go to make those strengths and weaknesses, they'll throw in a sequence of descriptive words without really considering how those words correlate.
A character's strengths and weaknesses are not dissociated. In fact, they are intimately related.
I'll use the most obvious example-- think of a character creator. Now think of the kind of character you want to make-- let's say a Warrior. You want to crank up their Strength, but when you do that, you have to take points from other fields. You may decide that, since they're a martial class, you're going to tank their magic stats, so you reduce their Magic and Magic Defense (or whatever stats drive those) and put those points instead into Strength and Defense (or Constitution, or whatever it is in this system). Maybe you allocate a few extra to Speed. Whatever the case, what you wind up with is a character who excels in martial combat, but can't use any magic attacks -- or at least can't use them to any efficacy -- and who is weak to magic damage.
In story terms, this mirrors a warrior who has dedicated their life to the blade. They are excellent in martial combat, a master of their weapon of choice and competent with a handful of others, but because they have spent that time on weaponry they have NOT spent that time on spellwork. The character may be very intelligent, but they've not had a chance to study magic in any competency, which may prove difficult in certain kinds of combat and may prove equally difficult when it comes to untangling the arcane. You can take this even further in this example; perhaps they are a master of the blade, and competent with swords, but if you hand them an axe they won't know how to wield it properly. They'll be better than pulling a guy off the street, sure, but an axe is a completely different weapon than a sword.
Maybe you want a jack of all trades. So again, consider the spread-- if you don't specialize in anything, you are at best competent at everything, able to slot in to any party configuration, able to fulfill any role... but not well. This too is a strength and weakness tradeoff-- significant adaptability, in exchange for not being exemplary at any one thing.
Now we can apply this to character who aren't necessarily fit for a DnD campaign. Let's go back to Bonzo. He is handsome, charismatic, and intelligent, but his pride prevents him from being able to allow others to use their own gifts and he demands they adhere to his strategies or else they will be punished, as Ender was. If he had been able to confront this pride and learn some humility, he might have been an excellent Commander rather than a middling one. At the least, he wouldn't be dead.
Since I'm on Card, let's also look at Bean, another character who, frankly, was ruined by his own book. Bean is introduced in Ender's Game as being extremely clever -- at least as smart as Ender -- but by the final games he is noted as being excellent with a small group, able to command an elite force like a scalpel but unable to work with a full army. This is very fair. Meanwhile, over in Shadow, Bean is actually smarter than Ender, and even younger, and actually just as good with people but he just chooses to lose all of his battles in Battle School. During the final games, he not only figures out what's actually going on through a completely random comment that he somehow spins out into realizing they have faster-than-light communication (when the kids have been told they are going to launch WITH the ships so of course the time-lag won't be a problem?), but when he confronts the adults about what they're doing he's told that they are intentionally giving Ender bad information about Bean and that's why Ender comes to his bad conclusions about his abilities. Bean never had a weakness, he just wasn't allowed to show off his strength!
This flattens Bean. He was a scrappy underdog in Game; now, in Shadow, he's the best and most clever and everybody loves him and his only 'flaw' is that he's underdeveloped, which gets blown out the window in the sequels anyway. Bean is no longer an interesting side character with his own texture and utility and attendant flaws, he's an ubermensch who basically never has any real obstacles to overcome, and I don't like him.
A character's strengths and weaknesses should intermingle and inform each other. What a character has dedicated themselves to mastering is going to tell you the things they had to forgo to reach that mastery. The aforementioned warrior, for instance? A lot of interpretations will generally have this character be brutish or dumb, but he might well be very clever, he just never had a chance to study books so that cleverness turns instead to combat mechanics.
We can actually look at Sokka, from The Last Airbender, for a great example of this. His weakness, within the universe itself, is that he's a normal in a world where all of his friends and enemies can basically perform magic. This is an external problem, but it festers into internal complications-- he has an inferiority complex, and trying to prove himself can get him into trouble. But it also forces him into adaptation, and by the end of the series he has proven that his own intelligence -- previously turned to a defensive humor and sarcasm -- can be routed to martial strategy that Aang, Katara, and Toph are simply unable to match.
Your strengths and weaknesses should feed and inform each other. They should not exist in a vacuum.
Similarly, they should comport with the character's actual lived experience.
I'll go back to Sokka. Why is he the way he is?
Because his dad left and took all of the men of his village, leaving him -- no older than twelve at the time -- as the oldest male in the village, responsible for keeping the village while the men went off to a war they couldn't be certain they would return from. In this environment, Sokka had to learn to be quick and clever, had to rise to a station he had no business stepping up to at such a young age. This gave him a protective streak that both proves to be vital and also a little damaging.
You remember how Sokka was also kind of sexist until the Kyoshi Warriors put him in his place? This wasn't a random flaw of his personality; it was because he had been tasked with so much responsibility as the village protector, the last man of the tribe who was going to protect the women and children. This was a responsibility he had shoved on his shoulders far too young, and had no male role models to teach him the right way to channel his masculinity.
This is his core wound; the defining event of his life that informs his decisions and character going forward. Sokka's flaws and weaknesses can largely be traced back to this moment of unfair responsibility. He had to learn to take responsibility, to be brave, to be strong, that he was the only thing between invaders and everybody left in the village was relying on him.
(Bear in mind that when it comes to development, there's no right order; as I've said before, I tend to make characters who fit into the needs of the narrative and then determine what kind of person would wind up in this situation. My development tends to ping-pong in this way; what do I need them for, where does that mean they've come from, what else does that inform about them in the present day? And of course, nothing needs to be set in stone, if you prefer not to work that way; some people like to have their whole backstory and trait list laid out for them, but I personally prefer to know who they are and then fill in as necessary. Traits I might not have expected will emerge from situations I don't expect, which may inform an event I didn't think of, which will have an impact on another current-day issue that I hadn't anticipated. A recent revelation I had was that I made a particular character infertile due to Circumstances; this was just a consequence of cosmology, but once I started digging I realized that this had substantially broader implications to his psyche than I had anticipated, which was quite a fun discovery.)
To break this down again: because Sokka was left with so much responsibility, he had to learn to be brave but also clever, calculating acceptable risks. He taught himself how to lead by trying to teach the younger kids how to fight; it didn't work out very well but it endowed in him the eventual skills he would need to command disparate armies on the Day of Black Sun. He became a protector because he was the eldest male in the village, which taught him that it's a man's job to defend women, a fine enough ideal that curdled into benign misogyny because it was also fused with his inferiority complex, developed both by having to live up to his father's example and that his sister developed waterbending while he just throws boomerangs. A sister whom he was also tasked with protecting, because their father had left and his mother was dead, causing him to be overprotective of her until he saw how well she could handle herself, and thus shifted from protective instinct to trust. And this inferiority complex further informed his humor, which he weaponized into sarcasm and a defensive mask, and which itself masked the underlying cunning and intelligence that would eventually bloom into his strategic abilities. All of Sokka's core traits can be traced back to his wound, and then interlocked with each other, creating a well-rounded, complex, and endearing character from an archetype who seems at first to just be comic relief.
It's important to note as well that these flaws are not shaped by society. Sokka's virtues and failings were augmented and sharpened by his wound, but this is always who was as a person. I see too often that an author will give a character a 'flaw', but that flaw is actually an imposition by the circumstances of their life or the society they're in rather than a true, internal conflict. Maybe a character is nasty and closed off to everybody they meet; this would normally be a flaw in any social situation, but then the author reveals their tragic past and abusive parents and suddenly their nastiness isn't their fault, it was Society.
This isn't interesting. This isn't going to give us ongoing internal tension; this is just priming us for an endless cavalcade of a character being constantly forgiven or excused for their behavior or failings because external factors keep them down. And this isn't even to say that external factors won't keep somebody down, but how somebody responds to adversity is just as important as that adversity. Sokka could have begged his dad not to leave, we would have even understood if he had, that's very reasonable. But he didn't. Instead we respect him for trying to live up to those expectations even though he absolutely knows he cannot. This tells us just about everything we need to know about Sokka in one fell swoop.
In short, when you're crafting your character's basic traits, keep these three factors in mind:
1. Strengths and flaws inform each other
2. The character's backstory should be kept in mind or tailored to support them
3. Their flaws are not the fault of society