All villains are overconfident. This is even more so if the villain is uber-sexy. No one wants to hear about a bad guy with self-esteem problems, after all.
The only purposes for rain or storms is for a sappy romance scene, to warn of danger nearby, or to herd your characters inside a conveniently-abandoned-yet-still-standing house for some hot sex.
It is preferable that detectives are either ex-cops or self-assured women. Even if cops are trained to work in a team rather than alone and women are too physically weak, even with training, to overcome a group of burly men on her own, it is best if you have one of the two as the detective in a story.
Any kind of blade weapon (ex.: swords, carving knives, daggers) is easy to sneak into a high-security place. All you need to do is to slip it under your pant leg, and - poof - it's completely hidden, no problem! Uncomfortable? Odd bumps in clothing? The actual practicality of it all? Bah! It's cool, and that's all you need to make it happen.
Yes, your character can be 6'8", 130 pounds, and be only 12. C'mon, it's fiction, so anything goes!
No one has black hair and brown eyes in Japan. Really.
In any school where uniforms are required, the girls, if they have reached puberty, wear skirts that barely cover their butt. White shirts are common for both sexes. No, a girl's bra does not show through the shirt unless it's wet, no matter how the light is shining or what color the bra is.
There is no such thing as zits in the fictional world. They simply don't exist. Neither do moles unless it's meant to ugly-fy an old woman or act as a beauty mark on a Russian supermodel.