when Tricia asked me for revisions, one of the things she wanted (which I totally agreed with) required adding one or two new characters. I'd never actually done this before, and I was afraid the new characters would feel flat or tacked on. Here's what I did to avoid that:
1) Define the character. This is the novel that got me my agent, so the existing characters were pretty fleshed out. I wanted to make the new characters as deep as I could -- goals, motivations, even voice -- before I changed a word. (Yes, I planned. What a shock.)
2) Plan what needs to change. I skimmed through the entire novel, making a note of every scene where the character could appear, and maybe what that would do to the scene or the whole plot if they did. Sometimes this led me down some really interesting roads, though other times I realized it would mess things up too much if they were around.
3) Write the character. For each scene in my notes above, I had to decide whether or not they did appear. This was tricky. I didn't want them to appear only in the scenes where they mattered (no chance for development that way), but I also didn't want them to have a cameo in every single scene just because I could. In the end, I decided to keep them in most scenes rather than make excuses for why they weren't there.
Ah, but how to add them . . .
3a) Dialog. Sometimes the new character had new things to say, but most of my story was already set. Honestly, about two-thirds of the time, the new character just said things that other characters had said. I just changed the tag and the flow of conversation to support it. You'd be surprised how often -- especially in group scenes -- you can swap lines of dialog around without affecting things.
3b) Narrator descriptions and thoughts. Whoever's head we're in needs to notice the character. Not just notice them, but have feelings about them that affect things. Otherwise why have them there at all?
3c) Let them shift the plot a little. I wasn't about to rework whole plot points for these characters, but their presence did change things a bit. Partly, this is what they were being added for (to add emotional weight to certain of the protagonist's decisions), but a couple of events took me by surprise. It's usually good to let these things happen.
3d) Treat it like a first draft. It's so, so hard to add words to a novel that I know works (see the part where it got me an agent). I want the new words to fit seamlessly with the old ones and to be just as awesome. But it's better to accept that they won't be at first. You'll make them good in a second.
4) Read the whole novel again. Slow. Now that the characters are in there, you have to make sure everything still flows. It's not just about continuity and details, but you have to look at the emotions of the scenes. Do the character's words and actions fit what's going on around them? Is she being flippant when she should be scared, or crying in a relatively tame moment? (Mine was).
I also realized there were places where the protagonist could be thinking about the new characters, even though they weren't in the scene. The new characters were now part of the protagonist's life, and I think this helped make them even more real.
5) Send it to a beta reader who hasn't read it before. You can send it to betas who have read it too, but I wanted someone who knew nothing to tell me which character(s) they thought I had added, which felt the most tacked-on.
I was kind of excited when my beta reader named characters that had been in the novel from the beginning. It did make me wonder about those old characters a little, but the new characters felt like part of the story to her, which means I did it right. And honestly, now I can't imagine the story without them either.
Have you ever added a character in revision? How did you do it?