P = Princes/Princesses are often the heroes/heroines in fairytales of course but I love the heroines that prove themselves every bit as capable and intelligent as any hero (and are often better! Think Fiona in the Shrek series basically!). I also like those stories where the characters here have to prove themselves worthy of their calling - i.e. it doesn't just all fall into their laps because they are royal. A character who has to work for something, regardless of their background, is a character that will face conflict, dilemmas, enemies, and will make mistakes and basically give the reader lots of lovely action and drama to follow - and they will.
Q = Questions. Not such a tricky letter to find an answer for here though as I write this I don't know yet what I will be coming up with for X! All characters should ask questions and make your readers question them. The situations you put your characters in should test them (and make them query whether they are doing the right thing or not - internal conflicts like this add depth to your stories and make your characters seem more real. We all have internal conflicts to deal with so why shouldn't fictional characters do too?). Your readers should be engrossed with what your characters do and their attitudes and perhaps question themselves as to whether they'd act that way or not. A reader that is asking questions like that is one who is engaged with your characters and stories. You want lots of those!
R = Reading. It goes without saying we need to read widely to know what it is we like and what we would like to write as a result. But what would your characters read and how can you use that to show something of their personality? What are their world's myths and legends?