1) The degree of connection is important. Obvious, right? Down to the next point if you will.
Still, it’s a problem I’ve seen in several novels, most notably big epic fantasies. Several plotlines cluster around a single city, or a single family, or a single magical object, or are set in widely disparate locations but linked by mentions of their main characters being political rivals/allies/enemies with characters in the other plotlines. And then, alllll by itself off in the corner, is the story of a man in a mining camp near some mountain range unnamed on the map, who’s apparently doing nothing more than wandering around, banging his pick into rocks, and having a boring love affair.
This is a variation of a problem that can happen with proliferating viewpoint characters, I think. Create a character simply to be “eyes on the action,” and they often end up with no personality, attraction, or real interest. Likewise, create a plotline that’s supposed to dovetail with others several hundred pages down the line, but has no apparent connection with the rest for those several hundred pages, and it often ends up a distracting, irritating mess.
Establish connections between all the subplots and your main story arc. That’s really the only way I can think of to solve this problem. If you can’t think of a way to do so, then get rid of the subplot. Whatever it’s doing there—providing character backstory, exploring the laws of magic in your world, leading up to the release of a Dark Lord—can be done later and better with those subplots that are actually nestled into the heart of your world. For example, if the miner is going to meet the other characters only after he’s discovered a mysterious red rock that gives him ultimate power and traveled to Altra-Rome, why not have him enter the story with the rock at Altra-Rome? The important parts of his personal life can be told in flashback. We don’t need to hear all about his days digging for unimportant rocks and falling in love with a woman who never gets mentioned when he joins the rest of the cast, because by then she’s dead and he can’t bear to talk about her.
If it’s not connected, it doesn’t need to be there.
2) Subplots can have the power of concentration. Precisely because they’re sub-, they don’t get as much room as some other aspects of the narrative will. So you can write them as high points, intense moments, or key character epiphanies.
I tend to think that fantasy novels, in particular, have a lot of flab. Extraneous exposition is the culprit I usually name, but it can also be found in worldbuilding details that use seven hundred words where one hundred will do, character “introspection” that repeats the same issues addressed every time the character sits down to monologue, mysterious confrontations that delay revelations for no good reason, romantic angsting of the “I love him. Does he really love me? (Note that I am too chickenshit to actually ask him).” variety, and road trips to every single city or country on the map. It’s bad enough in the main plot arc. But at least there the author takes room to spread out with some reason. These are the characters we’re supposed to care the most about, the aspects of the world we’re supposed to pay the most attention to. And all the things I find boring can come down to matters of personal taste; some people hate battle scenes, for example, while I often find them exciting. At least I can know the author is taking time to fight the battle because she took time to build up to it. Perhaps the buildup wasn’t the most exciting part of the novel, but I know why it was there.
In subplots, I have no idea why the hell the flab is there. The secondary romance only has fifty pages out of six hundred to develop? Why are you wasting time with angsting and the characters having nightmares that don’t advance the plot? HELLO. Aren’t they supposed to be falling in love? Where is the love part? Sometimes crammed into the last ten or five pages out of the fifty, or, in the worst case scenario, into the epilogue; we’re just told the characters fell in love and decided to get married, because they were too busy running the hell around to actually meet. (J. V. Jones, in The Barbed Coil, before you think I’m exaggerating).
Cut out the flab in subplots. Choose what needs to be told, of course, but wrap it in good, intense, concentrated storytelling. By virtue of the way you’ve chosen to plot the thing, you don’t have room to sprawl here. So remember that brevity and depth, not length, are your subplot friends.
3) You choose ‘em, you weave ‘em. The weaving metaphor is in honor of the single most common phrase I’ve seen to refer to subplots in reviews: “dropped threads.” The author creates these stories of revenge, or secondary romance, or minor character arc, and then refuses to acknowledge them. They get snipped off so she can continue weaving the grand tapestry.
Keep track of your subplots. This is another reason why it’s a good idea not to have them proliferate all over the place. If they’re so numerous that you actually forget them, something is wrong. If nothing else, they don’t have enough inherent interest to remind you of their presence all by themselves? That’s a tremendously bad sign.
Most of the time, though, I don’t think literal forgetting is the problem. It’s the rushed ending again—I may have mentioned that I hate those—where the author suddenly realizes she doesn’t have enough time to tie up both the main arc and the subplots. People will notice if she just stops her main story in midstride, though, so she tends to that. The subplots are orphaned.
*Limyaael thwaps author on head with a stick*
An author may not have full and complete creative control of her story. Having had a story twist and change on me, I am fully willing to believe that. But the author is not her story’s slave, either. If she writes a first draft in which subplots are dropped, she can, revolutionary idea that this is, go back and fix it. The ending can be expanded to actually mention what happened to Character A, last seen tearing off into the great unknown to chase down her mother’s murderer. Or, if the author can’t do that because of wordcount limits, she can snip out the unnecessary subplots. Shift the burden of the action onto other characters. Cut out viewpoint sections by people who vanish from the story, and find some other method of conveying their information. Seek scenes that repeat each other and destroy the less interesting variations. Add throwaway lines to some slower-paced areas to mention what people currently offstage are doing. Take character arcs that will never come to fruition anyway—the audience never does get to see these two people fall in love, or Character A come to terms with her mother’s murder—and streamline them so they don’t demand as much emotional investment. Extra depth to secondary characters is great, I’m all for it after reading stories where the protagonist is the center of the narrative universe, but extra depth that the author doesn’t care enough to finish sketching is useless.
4) “An eerie resemblance” is not the same as “identical twins.” One useful function of subplots is ringing the changes on a theme. Say one of your major themes is vengeance, and you want to do more with it than the “character hears lectures on how vengeance is empty and will fill his mouth with ashes, character laughs at lectures, character achieves vengeance, character realizes vengeance is empty and has filled his mouth with ashes” thing. So in one of your subplots you show a character achieving vengeance and being happy about it, and in another vengeance occurs but doesn’t help because the avenger really wanted something else.
Now, do you need two subplots in which the vengeance theme is played out in exactly the same way? I don’t think so. Those are the identical twins, and they’re taking up time, page space, and reader and authorial attention that could be better focused elsewhere. Also, most of the time one is stronger than the other, but the weaker one not only slows itself down; it clings to and puts drag on its swifter twin by the sheer sameness between them.
There is one possible exception to this: where one subplot will twist violently near its end and reveal that it isn’t really the same thing as its twin after all. However, keep in mind that if there are too few differences along the way, your readers might well cease caring before they reach the twist. (This is another strike in my campaign against revelations that are delayed too long and for no real reason).
5) Try doing things with the characters, narration and other elements of story in the subplots that you can’t with the main arc. What you can do with the plot in subplots is, of course, restricted by the degree of connection they need to have with the story, their limited page time, and other things I’ve already talked about in the other points, all under that annoying “sub-.” But just because these are secondary characters does not mean they need to be copies of the main characters. More worldbuilding might take place in subplots than in the main novel, if that’s what the subplots are there for. And, in fact, in at least one important respect, the change of “plot” can apply to subplots. After all, not every subplot in a mystery story need be a mystery, or every subplot in a romance story a romance. It’s probably better if they aren’t, since such similarities can lead to a great deal of repetition, vagueness, and pointing-up of cracks in the author’s writing. On the topic of mysteries, I can accept one really clever detective in the main arc; I find it much harder to accept four, three of whom I don’t spend nearly as much time with.
At an extreme, even style can be varied. Perhaps the rest of the book is in third-person, but one subplot is in first-person. Why? Because the character needs a voice that distinguishes him. Because this part of the story is small and cozy, and better suited to the intimacy of the first-person than the more distant tone you take elsewhere. Because this narrator is a snarky, clever bastard, and it’s a lot more fun to be inside his head and hear all the insults he never delivers as well as the ones he does. There are all sorts of reasons.
I do think there needs to be a reason. Adding a first-person narrator “just because” smacks of adding the subplot about the miner digging unimportant rocks “just because.” There’s a fine line between luxuriating in your world and making it wider, and cramming the book full of threads that, once again, you stand in danger of dropping.
All I have to say on the subject for right now, as I’m pretty tired.