I need everyone’s best character advice. STAT.
You're not creating real people, you're creating the illusion of real people. You don't have to mention their favorite food if it doesn't come up, you don't even have to know it, though if they were actual people they'd have one. You can throw plot events at your characters to force them to take certain actions, or you could just rewrite the characters to be the kind of characters who would take those actions anyway. Your characters have a life of their own in their own little world, but don't be afraid to play god to get what you want out of them.
In the vast majority of cases, a character's strengths and flaws should be the same thing. There are exceptions (you can have a character be clumsy for the lols without needing to find some way that it's an advantage), but for most character traits, the difference between a flaw and a strength is the situation at hand and learning when to indulge it.
desire is the source of action, so your characters should WANT things. all of them should have something they want that's good for them, something they want that's bad for them, and something that's just a little silly, for spice.
Treat your secondary characters like they are the main characters of another story. I don't mean you have to know everything about them, but if their role in the story could be replaced by a cardboard cutout, then the story will feel flat where it encounters them. Give them their own motivation/wants/desires, and it will help you immensely in writing their interactions with the main character, and make the world seem bigger/more real to the reader.
Unlike real life, if you want anything out of your characters, you need to put them through meaningful hardship. Angst for the sake of angst is fun to toy with, but at the end of the day, there needs to be a reason for it or it's just not going to be interesting. Make sure that it's something that will get you more character out of your character.
