There are at least two schools of thought about writing a novel. One is that anyone can write a book. All you have to do is start typing words. The other theory is that writing (successfully, anyway) requires a talent not everyone has - wordsmithing, parsing, creativity, and a grasp of the components of good novels, and more. I lean toward the second school of thought, but I'm confident that the majority of the population subscribes to the first one.
Regardless, there's more to writing fiction than a fertile imagination, a grasp of how to properly structure sentences, paragraphs, and chapters, and a certain degree of literacy in a specific language. Like every other discipline, it's an endless learning process. In my case, I'm learning new things about the craft of writing every day.
Fortunately, in this very wired world, there are limitless sources available, and I've only scratched the surface. There are writers' groups that meet regularly to discuss developments in the industry and review and edit each other's works. If you can't find one that focuses on your chosen genre, form one.You can start by asking the Community Relations Manager at the nearest Barnes & Noble to put you in contact with local writers. Also, most communities offer adult education courses - online as well as on the ground. Depending on where you are in you development as a professional writer, you may want to participate in more advanced classes, rather than beginning creative writing courses. These are great places to obtain constructive criticism of your efforts. Just don't go in with thin skin or a firm belief in your own literary omniscience.
The 'Net is a great place to find all sorts of information, advice, and leads. There are some very helpful blogs, as well as websites for editors, agents, and publishers, and sites that offer reviews of the editors, agents, and publishers. There are sites that will plug your book to large audiences of readers.
I'm going to try to add a page or two to this site that will provide links to some of the sites that I've found to be helpful.