...if any of you have any advice on creating an original plot for a fantasy story, or even an idea you haven't seen done to death that you wouldn't mind sharing, please help!
There isn't a damn thing written today or in at least a few hundred years (probably longer) that hasn't been shamelessly cribbed from dozens or more sources. Character arcs, themes, plot devices...it's all been done, all that varies are the details and how the stolen bits are combined. You could write a fantasy novel with plot details that no one else has ever dreamed up and it could still be boringly derivative.
So, the greats steal, but they steal
well. Pull inspiration (steal) from unusual sources and put something together that hasn't been seen yet. A good example is Susanna Clarke's "Jonathan Strange and Mr. Norrell" which put a tale of magic and fantasy inside the very done to death structure and setting of a Victorian novel. Despite the clear antecedents, the book was fantastic and "original."
Write well, too. Even pulp can be excellent stuff if you develop your characters well and write clearly and vividly. It also doesn't hurt to have something to say. Explore themes that say something about the human condition. Don't just have another wizards and dragons fest with no point behind it. That's just fan service stuff, and it won't widely resonate.
So mine interesting sources. Look at obscure religious and cultural traditions for interesting themes and devices. A fantasy book I'm reading now uses Cornish mythology for inspiration.
Good luck too, you'll need it. Oh, and I won't share any interesting stolen bits, because I want to write my own novel someday.
