www.tvtropes.orgI discovered this website whilst being bored a few days ago and just now realized that this may help with one's roleplaying skills. It may be about television/film tropes, idioms, and "cliches", but reading it (which might take a while--they'res tons of articles) will help you avoid using Mary Sue characters, cliche plots, overdone backgrounds, and etc...
Each of the articles first gives you a description of their trope/idiom, then a (usually) massive list of popular shows/movies/games/whatever that has an example in it. Well, enjoy.
Here's some you could get started with (you should probably read each of these, as they're common in this game):
Freudian ExcuseBlack KnightEpiphany TherapyParental AbandonmentRape Is The New Dead ParentsDoomed Hometown