How do I convert a story idea into a full-fledged novel?

Okay... When I started with my Epic Fantasy, some of these questions took up a lot of thought. But I'll try to answer all of them for you. 1) I found it useful to know where the whole story is going. Not only in the book I'm writing, but in the series as a whole. Then I keep the sub-plots centered around things leading up to the rest of the story. I did it while drafting, since I couldn't actually plan the story out. You can either do the same or plan, depending on how you write. 2) Sadly, this is done by practice. Either while writing your story, or by writing random descriptive passages of various landscapes until you feel comfortable with it. 3) Once again, practice. Use what you can see and describe. And lighten up about this. No one will ever see a character the same way as you do. No matter how hard you try. The point here is to give the reader enough to go on. Tall? Short? Hair color? Eye color? Anything else that stands out to you? EG: if a character's not white, let people know. If the person's a punk with an acid yellow mohawk, let us know, because if it comes up later without warning, it'll confuse your readers. Because by then, they will have drawn a conclusion on what the character looks like. 4) Reading about strategies can be good, if that's what you're focused on. If you're focusing more on the main characters, you have a bit more leeway. 5) Blow-by-blow battles can be very boring. Blocks and parries are the same, although blocks stop weapons in place, while parries deflect them. But there's no point to being technical to the point where your readers need to research martial arts in order to understand you. Description is your friend here. "I deflected his blow and dodged to the side before slashing at his head." Much more understandable. 6) A lot of people create characters, but I can't really tell you too much about it since my method is a bit more unorthodox. I never start writing before the character doesn't show up. When he/she does, I assume he/she is fully formed and write as if I'm discovering the character's complexities, motivation etc. with the reader. Makes for some awesome characterization. Hope this helps!

Obtain pencil. Obtain paper. Obtain chair. Attach rear parts to chair. Determine which end of pencil creates a black line on paper. Create lots of black lines. Revise. Repeat until you have something someone else wants to read. Everything is theory until you have something to revise.  If you don't know what high cheekbones look like, then they are meaningless to your story.  Write what you know and the story will tell you what you need to know more about.

I think there are many authors that start by writing a short story and then find that it grows to too many pages. That's one indication you need to develop it further as a novel. If you have written a short story, you already know about the character having a battle with a personal or societal villain and the blow up comes toward the end. A novel will often introduce the stages of the conflict over many chapters, so it can build in depth i.e. personal conflict, family conflict, societal conflict, environmental conflict, etc. It often introduces related subplots via additional characters that face a conflict. Two books that can be helpful are the Writer's Journey by Chris Vogler and 20 Master Plots by Ronald Tobias can offer a glimpse into elements of a novel that you should have including: A hero; stories without heroes leave the reader wondering whether they care about the characters. A villian; without a villian, there is no conflict so the story will be boring so make it complete Some other rules of the road I've learned: introduce all your characters by the first 1/3 don't introduce new conflicts in the latter pages, often it leaves the reader thinking there was no story so the author dumped in some exciting things at the end make your character discover something about themselves because of the conflict by the end of the 2/3 of the book the last 1/3 of the book is really more like a chapter or two that resolves open conflicts don't discover technology, artifacts, people, social groups etc. that save the day at the end

To me it looks like you need to reframe your question:  I think what you're really asking is "How do I learn to write compelling fiction?" No one is going to be able to give you a definitive answer for that.  I adhere to the notion that writing cannot be taught, only learned.  Your job as an apprentice novelist is to learn the tools and skills you need to allow your audience to willingly suspend their disbelief for as long as they are honoring you with their attention.  One tool is research:  you cannot effectively convey something about which you know little or nothing.  One skill is self-editing:  you must be able to evaluate what you've written as if the words belonged to someone else and revise accordingly.  Also consider that novel-length may not be your forte.  Perhaps you'll do better with short stories or novellas.  Maybe you'd be more effective writing non-fiction.  As you seem entranced by the visual aspects of story telling, maybe you should consider writing a screenplay.  (The latter is cheating, in a way; you don't have to write a definitive action sequence, just indicate when in the script it takes place and let the director work it out with the help of her/his experts.) All writers are constantly striving to improve their craft.  The attempt may take the form of classes, workshops, and/or self-study.  There are thousands upon thousands of books on writing available.  A few I would recommend are: Associated Press.  Guide to News Writing Bradbury, Ray.  Zen and the Art of Writing Browne & King.  Self-editing for Fiction Writers Field, Syd.  The Screenwriter's Workbook Knight, Damon.  Creating Short Fiction Lyon, Elizabeth.  The Sell-Your-Novel Toolkit   Newman, Edwin.  Edwin Newman on Language:  Strictly Speaking/A Civil Tongue/Complete in One Volume Seger, Linda.  Making a Good Script Great   Stein, Sol.  Stein on Writing   Von Oech, Roger.  A Kick in the Seat of the Pants:  Using Your Explorer, Artist, Judge, and Warrior To Be More Creative   (Hie thee to Amazon or another good bookstore and look them up; you should never discount the power of serendipity in research.)   I just picked up but have not yet read Write Away:  One Novelist's Approach to Fiction and the Writing Life by Elizabeth George.  I admire her ability to sculpt language with a seeming ease that leaves me stumble-tongued.  Surely this one tome will be the key I've always sought to clear out the cobwebs and procrastinations!  (That's irony, by the way, and what I always say whenever I get any new book on writing.)   There are two more things I would suggest.  Read voraciously among those authors you admire and widely on all topics under the sun, and find a writing community (this isn't it) that will allow you the company of working writers of the type you would like to become.  Tall order, I know, but remember, if you can be discouraged from writing, you were never meant to be a writer in the first place.    And once you've learned from those who've gone before you, remember you have a sacred obligation to pay it forward.  The student must at some point become the teacher, and in doing so once again become the student.  Best of luck in your journey.

A fellow by the name of Stephen Byers released a book this July that has  been a huge help, Beginning Creative Writing: A Learning Experience, and might help you as well; the website is called  Booksbybyers, and I believe he is also on facebook, hope it helps!

There are some insightful answers here already, but I would add: READ. It sounds like you already do read, but go re-read Game of Thrones and pay close attention to how he describes things. The more you read this stuff actively picking up on the details and how the prose is formed, the more easily you'll find the words coming to your mind as you write. You may not be an expert in medieval battle tactics, but that's something you can research and plot out on a map before tackling in writing. What you really need is the skill of composing meaningful prose. And the only way I know to get it is by reading good prose.