I'm fairly passionate about writing, role playing, and I'm starting to become passionate about films. (Movies. So many good movies. So little time. o.o) So, that being said...
First: To define "originality", you need to first realize that nothing in the world is truly original and that the most culturally defining works (Romeo & Juliet, Star Wars, Lord of the Rings, etc) defined their genres by
being fairly unoriginal collections of mythos, concepts, emotions, and more, done well and/or subverted.
That's not to say that you can't have unique works, which is the word most people often mean when they say original. Just that true, 100% originality would be so alien as to be impossible to understand, and that originality is just another tool one can use to flavour a plot or world or characters, like garlic salt on steaks.
An example of originality is Mass Effects' "Mass Effect" fields. It's something to flavour the universe, which is a motley collection of tropes from the arbitrary "warrior race" (x2, one more Japanese and one more barbarian) to the "protagonist is a brick".
Second: If we define originality in this case as the "uniqueness" factor of a work, we can simply head on over to
TVTropes and figure out what tropes specifically are omnipresent in our writings. The moment you understand a stereotype or a trope, its strengths and weaknesses, what it does, and who it appeals to, you can utilize it in the future as a tool, rather than an accidental byproduct of a creative mind.
Third: With the first two out of the way, you can start on subverting plots. The first point is to make you realize that originality is not what you're seeking. Uniqueness is. Something to identify you from the swathes and crowds of other would-be GM's ruling over various worlds ranging from sci-fi to fantasy to supernatural to stuff you can't even categorize. The second point is to help you identify your strengths and weaknesses, and what tools you tend to use more than others so that you can end up subverting your own works if you want to. IE: Knowledge = power, that never changes.
Plot subversion can come at several points. It can come to the base level, where you can add as many letters as you want to represent additional parties over the conflict. Like a nations conflict might be built up as such: Players (A, B, C, D, etc) fight over limited resource/magical macguffin Z, in order to accomplish goal Y (power, glory, good, evil, etc). The beautiful part about this is that the limited resource can then be later subverted to turn out to be useless, unusable, or even simply never having existed and everyone having fought and murdered one another over legends.
It can come at a more "personal" level. Maybe the magical macguffin to defeat [insert evil here] is a magical princess... Only, halfway through the story, you do the unexpected and you axe off the princess. HOWEVER, you instead make it clear that only her blood was needed. Then you provide a couple alternatives, like trying to hide or seeking someone else who can defeat [insert evil here], a place where they can bring the princess' ashes to bring her back to life, etc. Then you have what is called a branching plot. This is something that some video game developers (cough Bioware cough) became (in)famous for: Providing choices, and allowing the players to take only one. This is when a plot starts to develop and evolve and become more complex all by itself. You don't have to do much, the players will do it for you.
Essentially speaking: A plot is merely a tool to do with as you please. You may subvert it any way you wish. The only requirements for a good plot are that the plot has conflict so that individual or collective parties can have a reason to do things to try and "win" the conflict in their favour, and that the plot is coherently logical and is believable enough to suspend disbelief. You can have a plot with ten opposing factions/characters/parties and only one conflict, or a plot with two opposing factions and a mind numbing ten conflicts if you like.
In role playing, you add another tenant onto that plot: That it's changeable, flexible, intractable. The players must be able to resolve the conflict, abandon the conflict, change the conflict, improve or damage the conflict, and otherwise simply be directly
involved in the conflict. If they aren't, the conflict has hand waved the purpose for having players, and the players will get lost, feel like they have nothing to contribute (because they won't), and will leave.
If you want to "study" and disseminate good plots, try watching Star Wars again. (I mean the real Star Wars, the original trilogy, not the new trilogy... Tumour... Thing...) See how many tropes get used. See how the conflict rises and falls. See what tools George Lucas and the co-directors and writers used. See the visual cues that the artists and cinematographers used to display the scenes and paint the characters. Analyze it. Don't be afraid to repeat scenes. Hell, don't be afraid to ask others questions about why X was used, or why Z was used in the manner that it was used. (Even ask me if you like.)
I could go into further detail about typical plot structuring (introduction, start point, rising action, climax, detenté, resolution) but that's less "good plot" and more "how does plot work?" So if you want to know, you may ask, but otherwise I won't include it.
At this point in time on RPG, if you want to make a good plot, that is unique and stands out, all you have to do is make it a good plot. Because right now, the vast majority of RPG's plots fail the basic litmus test for functionality, leave alone being "good" in having a believable, logical conflict. That's not insulting RPG by the way, that simply
is. It's a fact. My plots were crap for a while. I can't blame the majority high schoolers here for not knowing how a plot works, leave alone how to make a good one.
EDIT
To Clarify: For a good plot, you need two or more sides that have reasonable investment and interest in the conflict.
EG: A, B, and C are three kingdoms fighting over the land to declare WHO WILL RULE ALL OF CHINA!
You also need a conflict that makes sense and is believable. The bigger the conflict, the easier it will be to make sense. I wish I was kidding, but I'm not.
EG: A, B, and C are three kingdoms fighting over the land to declare WHO WILL RULE ALL OF CHINA! Because China is big and full of resources, and each of the rulers is descendent from the ancient emperors of old and each lay claim to the entire land!
Then, specifically for role plays, you need the interactive element.
EG: A, B, and C are three kingdoms fighting over the land to declare WHO WILL RULE ALL OF CHINA! Because China is big and full of resources, and each of the rulers is descendent from the ancient emperors of old and each lay claim to the entire land! The conflict raged for years without end, and then, one day, some heroes and villains rose up to FIGHT AWAY CHAOS AND RESTORE THE ANCIENT ORDER OF OLD USING THEIR POWERS AND PROWESS WITH MARTIAL WEAPONS!
Done.
