To write a story with length, depth and heart, to begin you don't just need an idea, you need inspiration. But you don't just need inspiration once to conquer the entire book, you need it throughout the writing process, the editing process, and the publishing process. Without inspiration you hit a wall, get writers block, and lose confidence in yourself and your writing.
Inspiration can come from anywhere. Recently, I knew where I wanted to go with my story but I had no idea how to get there. My inspiration for that fix is named Sarah and she helped me come up with a way to make the scene a little bit more dramatic and suspenseful. With just one idea she sparked many different routes to get the story going to where I wanted to lead it. Inspiration is everywhere.
Today's goal is to get to 35,000 words. I have little over a thousand left to write today to get there so that shouldn't be too difficult. I'm the type of writer that takes the scene in question the way I'm feeling at that precise moment. If I'm relaxed, I'll give it a nice fun vibe, if I'm a little peeved, I'll probably make someone get hurt or kill someone off entirely, if I'm loving the weather, oh, here's a nice description of the weather that just happens to be the same in real life as in the novel!
Find your inspiration that helps you create. Create anything, imagination is key to a life of happiness.