You're right about that, and examples include Rowling, Stephen King, Terry Pratchett, Douglas Adams, Frank Herbert...
And this -
is about the worst advice I've ever seen on here. I feel we should all chip in for some kind of trophy.
My first tip is, if you want to be a writer, read.
If you want to write comedy, read comedy; if you want to write romance... you get the idea. Every book is a learning experience, even the bad ones. I would suggest starting here - http://www.amazon.co.uk/Writing-Stephen-King/dp/1444723251/ref=sr_1_1?ie=UTF8&qid=1421280279&sr=8-1&keywords=stephen+king+on+writing. Even if you don't want to write horror, there's no denying that Stephen King is a great modern writer and knows what he's talking about.
My second tip is, if you want to be a writer, write.
I had an idea for a novel, and like you I was confident of its strength. Actually, I had several, and wrote outlines for most of them so that one day I'd get around to them. I wanted to tell my story, but didn't want to spend all the time becoming a decent writer. The bad news then is that if you want to write a book, chances are you'll have to write a lot of none-book projects before you get that book looked at by anybody that could make something happen with it. That realisation almost broke me.
So here's the good news: during my learning of the craft of writing, I discovered my love for it. I dove straight into my first novel and made plenty of mistakes on the way, but then every novel stamped on a page has required several drafts to perfect, so don't worry about making mistakes you can rework later. Look for short story competitions; SF used to run a monthly one with a 500 word limit and I miss it dearly. Short stories, or rather flash fiction, are great exercises to make a writer more concise. Write about everything; record your dreams, have a nosey at conversations, describe the last person who walked past your house (what they were wearing, their body shape, the way they walk, anything different about them to other people. Try to imagine what they have in their pocket, where they're going, did they look at their watch? Maybe that's because they know that in a minute or two the police will discover the bodies...) Write it all and while you're doing it you might see a chunk of a character right there in front of you. If you like the way someone you meet laughs, or a figure of speech someone keeps using, jot it all down. Characters for me tend to be bits of dozens of people I see on telly, at work, and often enough in the mirror.
I am currently studying creative writing, usually at work (security guard is THE best profession in which to be a writer) with a part time course from OCA. Look here - http://www.oca.ac.uk/courses/writing-courses.html - and don't dismiss the idea out of hand, I have taken a very reasonable student loan to pay for the course, and the rate of learning can be fast or steady as you like.
As far as your story being overly complicated, try writing a synopsis (a google search will let you know how). If you can keep it under 125 words then chances are that it's fine.
A couple of extra pointers which are essential from word one.
Show, don't tell - this is the writer's mantra, and is what separates a story from a list of instructions. Don't say that the room was cold, show that she pulled the blanket tight around her shoulders; don't say he had a bad temper, show that he tutted then repeated himself slowly to the receptionist. When people wonder what makes a good writer, from what I can tell, story has very little to do with it; it's this that does it.
My last tip is that you should write how you think. The first time I put finger to keyboard (the modern version of pen to paper) I began by saying that "...exquisite sensations of lightning fire drove the weariness from his arid mind". I thought I was dead clever anorl. Turns out that fancy, round the garden writing like that is no use to anybody. When people read they want to get it in one go. Nobody wants to have to redo the same sentence over and over because it's too complicated to sink in on a scan. Don't try to look like a writer, just write and you'll be a writer.
Let us know how you get on.