Most writers don't just decide to write a novel and go at it. On the flip side, writers rarely just get successful from following their muses and writing whenever the inspiration comes. I can tell you right now that that doesn't work well towards getting anything done.
Don't get me wrong. You can have seemingly random ideas that begin to grow, but you have to give your ideas a lot of thought. They need to make logical sense and fit together so that you have a well-ordered plot. But before you start thinking of plots and mysteries and motivations of your characters, you need to warm up.
It's quite possible that, if you're an aspiring writer, you've spent your whole life warming up. Most writers are people who love to read. I certainly do. It is true that you should read widely. I have heard this particular piece of advice many times. However, I find myself turning back to old favorites. I don't fear change, but I do know what I like. So what fiction have I enjoyed? My favorite classics are Dracula, Journey to the Center of the Earth, Treasure Island, but I've never read Pride and Prejudice (saw and loved the 2006 movie, though). I love watching Star Wars and Shakespeare, and The Barber of Seville isn't too bad either. I read the entire Twilight Saga and enjoyed it. I've read through Harry Potter twice, and they make me laugh while they tell a good story. I like reading the fairy tale renditions by Gail Carson Levine, and the young adult Christian romance created by Robin Jones Gunn holds a special place in my heart. My staples are The Lord of the Rings and the Inheritance Cycle. I tried a Stephen King book once, and I didn't care for it, because of his content and his style. Jeff Smith's Bone series is phenomenal. This list could go on forever. As you see, my tastes tend to lean towards the fantastical. All of those authors are very different. All of them have flaws in their stories because they are human. Reading books that I'm unfamiliar with at first usually results in a new favorite, a new member of the exclusive club that is my bookshelf (and the guidelines are stringent).
So what does reading do for me as a writer? It means that I get a great example of how to tell a story. Jules Verne's writing is a very different type than Stephanie Meyer's, but they both knew how to put a plot together that keeps their readers riveted to their stories.
Read widely, but find what you enjoy. You may not enjoy everything in a certain genre. I certainly don't. I often rent a book from the library by an author I like...and become disappointed when I can't pay attention to the story. I avoid most high fantasy because there are so many illogical clichés. I don't read science fiction, generally, because the setting usually overshadows the characters and plot.
Please don't misunderstand me. I'm not saying that you need to find a niche and stay in it, never leaving your comfort zone. What I mean is that you should write what you know. If you think horror will sell for shock value, but you don't know it or are not comfortable writing it and have a hard time really making something scary, then you're not going to be a horror writer. If you like mysteries and thinking things through, go for mystery, but don't be afraid to mix it with another genre that you also know. If you find yourself wanting to read something that is not on the shelf at the store or library, then write it. Chances are, you're not the only one that is looking for something to read.