I did a guest blog for Maria Zannini on Thursday on tips for writing suspense.
One of suggestions I made was to never ease up on your protagonists; to keep dogpiling them.
One of the people who commented complained that she was having a difficult time keeping her heroine and hero angry at each other.
That comment reminded me to say something about the nature of conflict.
Conflict does not equal angry spats between the hero and heroine. Manufacturing reasons to keep your protagonists angry at each other is not the same as having true conflict--obstacles that prevent the two from their "happily ever after."
If you start down that road, you'll find yourself creating misunderstandings that will feel artificial.
Conflict can be either external (events occurring in the plot) or internal (struggles within the protagonist: i.e. an endangered goal or an overwhelming anxiety).
When you're planning your novel, think about who your protagonist is--what are her goals and motivations? What is her greatest fear? What is the biggest obstacle she faces--both in her mind and in the world around her?
I tend to write two parallel storylines in my novels--what I think of as the relationship plot and the suspense plot. If the relationship is going smoothly, I create obstacles occur in the secondary plot. If the secondary plot is humming along, I look for conflict in the inner lives of my protagonists.
Throw genuine obstacles in your protagonists' paths; don't fall back on petty sniping between the hero and heroine. I promise, you won't regret it.