My friends have exposed me to a lot of fun games that I'd never played before. Games like Small World, Settlers of Catan, and Chrononauts are great ways to spend an evening with good people. One of the things that I always remark on is how balanced the games are. There is a combination of random luck and strategy involved in playing, getting an early lead does not allow somebody to breeze through the rest of the game, and no single component overpowers any other part of it.
It occurs to me that this is a good lesson for more than just making board or card games. This is good advice for writing, too. What fun is a character who can't die? How boring is a character who never fails? How boring is a character who always fails? It is the not knowing what to expect that makes things exciting. Giving characters that same kind of balance, not having any one of them be markedly and assuredly better than another, makes for the most interesting stories.
Of course, this is not new advice by any means, just new words. The classic way to describe boring, predictable, overpowered characters is Mary Sue. And really, the advice here is all the same advice you see when reading how to avoid making Mary Sues (and why they are a bad thing in the first place).
Still, sometimes new words are all we need to spice up old advice. How balanced are the people in your works?