So you wanna write your first book. Whether you are a seasoned writer or someone who's been too scared to pick up the pen since high school, you still need the same thing to make it happen.
Yup, to write a novel, you need to push away that awful thought that happens every two minutes that you are a rubbish writer. Professional writers often have this problem worse than newbies. Accept that this is par for the course and every time you hear that voice telling you to quit, tell it you're writing the first bad draft of a book, so of course it's rubbish. Your first draft is supposed to be trash. It's the draft where you figure out what is working and what isn't. It's not supposed to be good.
So get to it. Embrace delusion, terror, self-doubt and anxiety... and start writing.
This is how a novel is born.