The over-confident always get their comeuppance. If only that was true in life!
Judging by Appearances
Basically, don't. Look at how often cartoon characters get it wrong and end up landing themselves right in it. Amongst others, consider what happens to Wily E Coyote, Elmer Fudd (when after Bugs Bunny especially), Yosemite Sam, Sylvester and Inspector Clouseau (from the Pink Panther cartoons. How often does a film spawn a successful cartoon series?).
Spotting the Villain
According to Scooby Doo, it nearly always is the caretaker.
Spotting the Unlikely Hero
The obvious candidate for this is Hong Kong Phooey (the mild mannered janitor turned secret super hero) though I always felt sorry for the cat sidekick for doing most of the work and getting little of the credit. That does reflect life!