Same with , I've written numerous books as well, and it's not easy to pull off. You really have to keep a story moving with some much-needed ambiance, and your narrative has to be incredibly dynamic, as it can't just be flat.
Although I agree with his 'double-sided personality' idea, one-sided stories are just as interesting. Some examples are 'Fatherland', 'Love Was Never Mine', all the detective novels (Sherlock for example), and so on.
Also, don't over-complicate your story by adding TOO MANY characters, as the plot will overlap itself (and that could lead to some pretty disastrous collisions). The characters could just appear as foil, or filler. They could also simply be subsidiary or non-existent to the plot, but make sure you know what you're doing if you're going to add characters to the main plot. I'm taking superhero novels out of this equation because Marvel and DC have a LOAD of characters (and if that's what you're heading for, then be my guest).
This is just some tertiary feedback based off of my own experience as an author, but this is your story, so I hope you make a good one!