For a novel or story to work you have to have relationships between your characters. I don't mean just love affairs but how do they work with the other characters, both good and bad. I think a lot of TV and movies as of late, and maybe even books, have forgotten how this is supposed to work. Don't shoe horn the plot in, make sure the characters would do what you are having them do when they interact with other characters. Here is a few examples from my story.
1) Krom and Tarkil. Here are two polar opposites if ever there was. It's not that Tarkil is evil, completely, at the beginning, he just isn't the black and white sorta person Krom is. With Krom there is good and there is evil. No in between. So Tarkil, who rides that line and sees shades of grey, not just black and white, is an issue for him. Krom can't understand the evil Tarkil does even as he is working on the side of good. And Tarkil, raised in a world where no one means what they say, can't fathom Krom's black and white nature. During the four novels Krom and Tarkil butt heads, but I weave in the fact that each, over time, begins to understand the other. I don't make it a, "hey, now we are best buds because the plot says so," I work the growth of the relationship, with all it's bumps, in over time.
2) Raphael and Tarkil. The hate/hate relationship is just as important as friendship relationships. How does your main character interact with the antagonist? In this case it is clear from the start that both hate each other, but as the story progresses they hate each other even more until it builds up into the final confrontation. You don't want something where your bad guy meets the good guy/guys at the very beginning and the very end, unless you have a build up of why there is so much hate between them during the story, even if they aren't face to face. There doesn't have to be direct confrontations through out the story, but you have to show why they hate each other. Don't wait until the end of the story to do that!
My point is, don't forget to flesh out the relationships. They are an integral part of the plot and to a good story.
Happy writing!