I like to write mine after someone else answers because I am selfish and want to read what other people have to say more than I want to talk about my ideas, haha. Also it was really time for me to go to bed last night, but this was in my brain after my update process.
1. When an idea strikes, what's the first thing you do?
I usually make a list of major questions I have about the idea (e.g. "Why x?" "What happens if z?" "Why is Character B w?") and ideas on the overall theme. After that, I decide what types of characters need to be in the story, what their motivations might be, and how those motivations might change over time. Then I probably just start writing. In the past I would try to start at the beginning, but just writing what's interesting has actually been pretty helpful to me, because then I get to the heart of why I like the idea right away and then I can figure out how to build to the point earlier on than if I started writing from chapter one, page one, paragraph one, word one.
2. Are there any things you consider integral to your planning process? For example, Julie mentioned earlier in the thread that she often makes a banner when she's in the planning stages.
Characters and character arcs. I usually care more about the characters than the plot anyway, so I figure if they're solid, they can move the plot along pretty effortlessly on my part. Since I like to start writing and then plan along the way, I guess world building typically becomes integral to me (since it's a big part of my niche in fantasy land), but in the beginning, it's never really about that. I do have documents that talk about details like topography, timelines, legends, likely aspects of language, etcetera. Though I'm not full on Tolkien over here making up languages. I'm 100% Team "English for Your Convenience and Mine."
3. If you use outlines, how faithful are you to outlines? How detailed are your outlines? If you write first and plan later, how do you keep track of your ideas? Anyone go between the two?
I'm the worst at outlines. I don't like to use them, probably because mine are never very detailed. I think I said it once, but Kevin's first fighting chapter in PBox was definitely "Kevin's healing power is awesome as an attack. There are plants." and I only had that after I decided that Howie, Kevin, and AJ were each going to get a chapter to show off their skills. Which is... not much of an outline? The last chapter I left on for PNecklace literally has a comment on the Chapter marker that says: "X and Z hang out. Z and B have an important conversation about _____." And I only have that because part of it's already written and these scenes almost ended up in the previous chapter until what happened in the previous chapter was more interesting for longer than I thought it would take to tell that part. I definitely have pages of notes in google keep where I scribble down random things I think of, but it's only coherent for me. I think everyone else would look at it and wonder why I felt the need to write that down. Half of them read like me spitballing to myself, complete with things like "Omg, what if Nick forgot about their secret santa exchange, that would be hilarious!" or "(Hahaha, remember Sam Goody? So funny.)" It's like collaborating on the forum, but with myself.
4. What's the easiest part of planning? The hardest?
I like writing more than planning, but even if you take a "write first, plan later" approach, you still have to plan at some point as the story grows. I think characters are the easiest just because they're the part of a story I enjoy the most. If a story has a mediocre plot, but awesome characters, I can still usually get behind it. If the characters are only okay, the plot has to be really amazing for me. If they're both kind of crummy, I might hate read it while drinking haterade depending on who forced me to do so or how far I've gotten into a story when I realize it's not getting any better. The hardest is probably world building, but it can also be fun too. I love falling into a research time suck because I just love learning more about things I enjoy or learning new things. I guess, getting out of those time sucks might be the hardest part for me. That and knowing that anything I world build, I always know more than my readers, so anyone reading my stuff could see a snippet of something, but I have this whole other aspect of it that I have to plan and research and finalize because there can't be any plot holes. It's... a lot... but fun!
5. How far into the planning process do you know that an idea is definitely something you'll finish writing? Or the opposite, when can you tell if it should be scrapped?
In the past, I was pretty notorious for posting any old thing I wrote down, so I guess I never really know. It gets scrapped when I stop writing it? I think if I can clearly visualize the end, that's a point in its favor to get finished. This is the curse of pantsing, I suppose, I don't always know the end when I start writing. I usually get an end down by... chapter twenty? That sounds about right.
6. Are there any clear signs to you that you're fully invested in an idea, either early or late?
I've mentioned many times, including in the novel about my novel and the initial question post, that I'm a doodler. If I doodle a character, I will finish that story eventually. Like I have pages of old class notes where I doodled tiny, persistent PBox Nick. If I'm thinking about it enough to doodle it, it's basically permeated my brain. Hence why I can come back after a long hiatus and write a sequel.
7. Do you have a specific point where you decide you'll post something or do you just post everything you write?
I used to just post everything I ever wrote, but I think my plan from now on is that I need to be about 15-20 chapters ahead of the update because I think that will hold me more accountable and allow me to post more consistently than I had in the past.