This anon's opinion is that you should treat OC personality sections pretty much the same as canon/fandom character's personality section.
Don't just list a trait, like "brooding", relate their traits to something in their history. For example, "Name is prone to brooding, as when he went to the roof to think, after the fight". If an OC doesn't have a long history or backstory, then use hypotheticals to demonstrate personality. Like: "Name is the kind of person who would laugh when insulted, but would show less humor if his friend's or family were insulted instead; he's very protective".
Let their actions and choices form their personality, and vice versa. If they once reacted one way, and later another, be sure to explain why or how they changed. Like: "In the past, Name would rise to any challenge and was prone to fighting whenever insulted, but after the terrible fight he lost, he learned to control his temper. On a later occasion, he struggled to find the strength to resist taunts, but ultimately resisted fighting, and instead walked away."
Re: ORIGINAL CHARACTERS
Don't just list a trait, like "brooding", relate their traits to something in their history. For example, "Name is prone to brooding, as when he went to the roof to think, after the fight". If an OC doesn't have a long history or backstory, then use hypotheticals to demonstrate personality. Like: "Name is the kind of person who would laugh when insulted, but would show less humor if his friend's or family were insulted instead; he's very protective".
Let their actions and choices form their personality, and vice versa. If they once reacted one way, and later another, be sure to explain why or how they changed. Like: "In the past, Name would rise to any challenge and was prone to fighting whenever insulted, but after the terrible fight he lost, he learned to control his temper. On a later occasion, he struggled to find the strength to resist taunts, but ultimately resisted fighting, and instead walked away."