Ask yourself the following question: ‘What’s my story about?’. But, wait. Before you answer, what’s it really about? On the surface, your story might be about a female lifesaver’s sexual conquests at a new lifesaving club. But, underneath her sensual romp, your story’s really about female equality and your character’s struggle to work out her true place in a predominantly male environment.
If you want to write a novel -- any kind of novel -- this article gives you some great advice.
I love the above tip. Knowing what your story is really about gives your book meaning -- you can't write a strong book without it.