Ideas are important, of course, but probably not as important as you think. You have an endless supply of ideas floating around inside your head, what’s more important is actually doing something with them, and keeping yourself from becoming discouraged.
Too many people sit around not writing as they wait for the ‘perfect idea’ to appear. The one that no one has ever thought of before, that is perfectly amazing and original, and will blow everyone’s minds with how much of a genius you are. Well. I hate to break it to you, but no such idea exists.
Everything has been thought of before, everything has been done in one fashion or another. If you let yourself be held back by worrying about if its been ‘done before’ you will never write a single word.
Imagine if people in other professions thought the same way. Cooks would never cook anything, because every ingredient has been used by some other chef before. Architects would never design anything, because someone else has used that same window or banister before.
Instead, grab every idea that you like, from any source you find it. Mix them together in your own way and transform them into something of your creation.
Most importantly, don’t listen to the people who say ‘but that was done in X movie/tv show/book/dream I had!’ I’m not sure I understand the thought process of these people, maybe they think that every author or director goes down a checklist comparing every idea and concept with every other idea in existence, or maybe since they are waiting for the perfect unique idea that no one else has ever had, they think you are too. Either way, they are everywhere and should be ignored.
Ideas are cheap and plentiful. If you don’t have any in your head, read a book or watch a show and grab some from there. What is important is actually doing something with them. Pick an idea that inspires and excites you, and go with it. Take for granted that it’s been done before–that doesn’t matter. You will add your own voice and character to it and make it your own.
Just like a chef doesn’t have to use completely unheard of ingredients to create a new dish, you can use known ideas and concepts and blend them together into your own creation. What makes a great writer lies in blending those ideas together, and adding the spice of characters and details and environments and sights and sounds (yes, you can have a scene with a sunset, despite other authors having scenes with sunsets!) in a balance that makes it appealing.
So if you like an idea, write it! And if someone tells you its been done before, take a moment to let them know what a bizarre statement that is.