Characters are people. Do you know a single person whose flaws are limited only to the physical or to the mental/emotional? Probably not.
Okay, hi. I have a slightly different answer here. Though I agree with O that character flaws should run the gamut of physical and psychological imperfections, I want to stress that these “flaws” are extremely subjective. If we look at the examples you gave for physicality for example, many people do not interpret overweightness as a flaw, and there are people (not me*) who have fetishes for stretch marks and therefore do not consider that particular skin condition to be a flaw.
For me, physical characteristics can’t really be considered flaws. They are just the way a character looks. Giving a character who is otherwise perfect a bit of acne is not going to magically remove their “Mary Sue” status, if indeed such a thing exists. The relationship of character physicality to character psychology is more complicated than that. Better to set about creating a physicality for your character which suits the needs of the story you’re trying to tell than to think of height or weight or skin blemishes or crooked teeth as character flaws.
On to the psychological. If you feel your character might be too “perfect,” my suggestion would be to try writing out the attributes of the character and tweaking them a bit. An example:
You can easily make a “virtue” into a “vice.” All you have to do is have too much or not enough of that virtue. Let’s take another look at Lula. This time, we’re going to push two of her virtues off the deep end, over-stressing them to the point that they become vices. Observe.
Where there is too much self-confidence, there is pride, and if she is too brave, her rash behavior could get her into trouble. Now Lula is looking a bit more balanced. What else can we do? Let’s dial down two of these virtues a notch as well.
Neither virtue has become a vice, you see, but both are significantly less vague. A considerate character is nice and polite if possible, as opposed to a kind-hearted person who can be Snow White-ish in her sweetness and amiability. And loyalty demands allegiance in all respects while trustworthiness is merely reliable honesty. After toning both virtues down a bit, we have a less extreme and more streamlined idea of Lula’s personality.
Is there anything else to be done? Well, we could add more specificity.
intelligent→ avid reader
Lula isn’t just vaguely “intelligent,” a catch-all word that doesn’t tell us much about her as a character. Now we know that she gets her wits from the books she reads, but that she is also at their mercy. The books she chooses to read will shape her understanding of the world as much as they will distract her from it. With her nose in a book, she is less likely to experience “real life” but more likely to know the answers on the American Lit test next week. “Avid reader” gives us much more to go on than “intelligent.”
So now we have a Lula who is more rounded.
Though at times prideful and rash, Lula, an avid reader, is a loving, trustworthy, and considerate person.
If we know nothing else about her, we at least know that much. And, bonus! This is not a description of a “Mary Sue” anymore! Success! While we didn’t necessarily add “flaws” to Lula, we did drag her down from the lofty, positive-traits-only heights of perfection. She is a more rounded character. Ultimately, that is the goal.
We have a creakingly-aged section of WriteWorld devoted to character building that might serve this topic well. Though it is desperately in need of a revamp, our Character Virtues and Vices page might be able to offer you some character help.
We also have a guest article on this topic that is well-worth the read: Guest Article from Elizabeth: Switching Up a Too-Perfect Character. Check it out!
Thank you for your question!
*Okay, yes, it’s me.