Why is my first novel so hard to write? The cold hard fact is that we're not all trained professionals. There's a lot more to writing any book than meets the eye. Fiction is not like a step-by-step "how to," non-fiction has its own challenges related to research and citation. In all cases, you've got to know more about your subject than you'll ever put on a page.
At it's most basic, Fiction is storytelling. The structure of any novel will always be a matter of some debate (argument, etc.). There is no one "right" way to do this. There is, however, one thing to do that you'll never get away from. Chapters. All novels move/progress from one chapter to the next. Chater two leads in to chapter three, etc. I, personally, like short chapters that can pack a punch. Others like longer chapters that let them dig deep in to something-or-other.
That's why the writing process matters. It's also the one thing that tends to be such a pain for many new writers. Many of us never learned how to do this in a classroom, we never had to do it as part of our regular day job--so--we tend to think it's just not that important. The easiest way I know to develop chapters is to scribble a simple outline. When all else fails, tell your story on paper in short sentences. As best you can, summaries each major portion of the story in just one sentence, and you can have yourself a bare-bones outline before you realize what you did.
Having a road map of your story goes a long way toward keeping you on track when writing starts. Everyone deviates from their outline, there is no reason why you've got to be ironclad about it. thought processes often change based pm what you learned while being knee-deep in the book. Never feel bad about those changes, they can only work for you.
There is no requirement to write in a specific genre. Just tell your story and let other people decide for themselves what category to put it in. Some people really do know their genres well enough to quibble over story points. Let them be a picky as they like, it's your story--do it your own way. That's how new genres are created. Who you do think comes up with all those new villains, eh? It's the people who blended genres, or did something unorthodox.
that brings me to my last point. I like a good villain just as much as the next guy--but--always know your heroes/heroines. If possible, know more about them than you'll ever put on a page. Character development can make or break any story. As the creator of everything you write, it's up to you. Consider this: if you don't write it in your book--it didn't happen. Nobody knows that your heroine is really good a tap dancing--unless--you put it in there. In my opinion, these are the big picture issues that can make your first novel harder than you might guess it would be.