It's a rare novel that can manage to cleave to one plot and fill up the story with it, without stinting the setting or secondary characters, or making the novel feel thin. Such lovely complications they can give you.
But that also means that you have to decide where to put the events in relationship to each other.
Sometimes it's obvious. Everything that happens to the heroine while she's prisoner at the court of the Elfin King has to happen before the hero returns with what the Elfin King sent him after and can hold him to his promise. Sometimes it's less so. Especially when you're trying to finagle the climax. All the factions that haven't been destroyed or subsumed (a complication that challenges placing stuff in the middle) must come together in a grand explosion to crown the plot. Dealing with things one by one there, you have to figure out which to do first, which last, and which in the middle, so as to have no sense of anticlimax when the three subplots get tied up after the main plot.