A very simple way to make your story good:
Do NOT think like this:
'I will write a novel, but I need an idea'
Think like this:
'I have an idea, now I will write a novel'
But that does not mean you do not write unless you have an idea. You should write short things often (prefferably everyday) to make sure your skills don't go blunt. Write poems or do simple deive pieces to explore a tad more and keep the creaive process flowing. A large project such as a novel cannot be treated like something you could start think about once you've already started the project. I'm not one for writing, but in my opinion; it's better to treat all creative pieces in such a manner. A music piece, a painting, a novel... you have to put thought into these things.