After a very long sabbatical from this board, I have returned. This is a topic that I see come up all too often. What's the difference between being inspired by works and copying them? For this guide I'll use the Twilight series as an example, since it's the one I see most often.
You read Twilight and think "Wow! I want to write a story about vampires". This is where you can either choose to be inspired by the work or start to copy it.
Path 1: Inspiration
To be inspired by a work is to take elements that you really enjoy and incorporate them into your own work. It could be an author's style, subject matter, or message. This is often used as a jumping off point. After this point it's up to you to make it your own. Do independent research on vampire lore. Read other novels where vampires are central characters (I recommend Dracula and The Historian). Get a feel for what's already out there. You want to carve your own niche. Once you've done research and other reading, then begin to brainstorm. What makes your work different? Why would your work grab a publisher's attention? Make a list if you need to. I'd recommend having someone else read it and give feedback. It's easy to fall into the rut of thinking you're creating something new when you aren't. Which brings me to...
Path 2: Copying
This is where you take plot elements, characters, or themes and claim them as your own. This doesn't have to be intentional, but it still counts as copying. For example, you really like Edward's character. You change a few superficial details about him, like his name, hair color, and age by a few years. However, the personality of the character remains intact. You've just plagarized. Scary, huh? If your work ever managed to be published, you could be sued for plagarism. It's like putting on a mask at Halloween. You're still the same person, just obscured. M. Night Shaymalan was actually sued over "The Village". An author claimed that he had stolen the plot from her novel. He won the case, but it just illustrates my point.
To all of you reading this thinking "Oh no! Is she talking about me?". No, I'm not. I've seen a glut of vampire stories pop up all over the internet, not just on DDN. Most of them are basically a poor rewrite of Twilight. I love creative writing and I find it wonderfully theraputic. It's just important to distinguish between what inspires you and what you've copied.
NOTE: If you love a series that much, try fan fiction. Some of the best writing I've read comes from the fanfic universe. You still get to be involved with your favorite characters and you won't be a copycat.
