Which part of a spanking story to you find the most enjoyable to write?

I find the most exciting part of writing a spanking story is developing the original concept into the main plot, with the actual spanking somewhat secondary.

It is the same with reading a story, I find the build up is more exciting than the main event.

Mine is similar but a little different: I enjoy developing a particular between a psychological aspect (usually of what it takes to put oneself in the vulnerable submissive role...how it's resolved in one's mind) to the mechanics and details of a fresh theme or plot. With some stories, (even ones that superficially resemble nothing of my specific identity) I use my characters to almost therapeutically flesh out unexplored or unresolved aspects of my own past. And by 'past' I mean my very early years when i was so confused and torn by my desires as they related to the otherwise vanilla world I was firmly embedded in. This is why I've done a fair amount of "coming of age" stories. These types of stories end up being very personal to me.

For me, it's the time between when the spanking starts and the first smack lands. When the spankee is getting into position, the spanker is pulling out the implement, then the spankee suddenly decides to make a run for it and the spanker has to chance them down, that sort of thing. Or maybe the spankee submissively goes over the spanker's lap and offers their bottom for chastisement. Whichever. When done well, the tension is palpable.

This is also incidentally when the most focus tends to be put on the clothing the spankee (and maybe spanker) are wearing and sexy outfits are big part of the fun for me.

I love writing dialogue - developing characters, relationships, and plot through what the characters themselves say, making it believable (or at least believable within the "world" I've created for them, however much detached from reality).

I like the part when the essence of a plot crystallises in my mind, particularly when I have an idea and it is hamstrung by some lack of internal logic in the story or something which will stop the plot progressing. When I then think of a way to fix the plot hole or a believable way for the next step to occur this is the best bit.
I also like the part where I have an idea for a joke - usually a silly pun - and a means appears for it to be put in the story, for example, in The Tale of Gillian, a character in a Snow White-type situation explains that his engravings have been at the printers for ages and he just has to wait patiently for them - he says, "Some day my prints will come"

There's a moment(in fiction and in real life) where a normal relationship transforms into a potential spanking relationship. Where the spankee realizes that, despite all the reasons they shouldn't be, but they can and indeed may be spanked. From the spanker's side, the turn might be when they take the leap to open that door. The scolding, or the swat on the bottom. In real life, I've found the easiest way is to say something like "You know I can't let you get away with that." There's a magic in this space and it defines the spanking dynamics of certain stories.

That's my favorite part to write.

I don't have any specific favourite part, I enjoy the challenge of it, each part of the story contains its own challenges.

I like conjuring up a very believable description of how the persons found each other / discovered there was an interest in spanking, or if they already knew each other, what was the occasion / reason for the spanking(s). In my not-so-extensive experience, most people don't blurt it out. It usually takes some 'warmup' (pun intended) of getting to know each other, beyond blind dates and chit-chat.

I would agree. There are only so many ways you can write that "(s)he spanked/beat/whipped/thrashed/flogged his/her butt/bottom/ass/cheeks/hindquarters with [insert implement(s) of choice here]." The story has to capture the reader's attention and keep it before you get to the payoff.

To me it's all about the set-up; I want to avoid writing stories that appear too 'cookie-cutter' so I try to come up with something slightly different for each story. Frankly some were more challenging than others. I've written one SciFi and wasn't particular thrilled with the end result. I've written one poem and I don't see how folks like Jennifer Pearson and Alan Barr can knock them out so regularly. I can't remember if I've ever written an M/M story; obviously it wasn't memorable if I did.

I start with the overall big picture. Most of my stories involve parental figures. So, first decision is male or female spanker (or both), and same for the recipient(s). Then, is the parent disappointed, angry, frustrated, or an overbearing jerk who makes life hell for everyone? Is the 'victim' normally good but just fell off the wagon, been pushing their luck for a while, or out of control and need a knot jerked in their tail? Is (s)he repentant or belligerent about the upcoming punishment?

What did they do that got them in trouble, and is this going to be a lesson for the entire family or something handled privately? Finally, what will be used to tan their hides? I've tried to utilize more unusual tools like a martinet and a backscratcher and unique positioning of the recipient just for some variety.

Then I just start fleshing out the details from there. I work on multiple stories simultaneously rather than writing a single one from start to finish. And often the finished product varies significantly from the original outline. But writing the actual spanking portion is less enjoyable than the set-up to get there.

I like the set up, particularly when I'm thinking of it. I've got about 4 stories in progress right now, where the set up is done, and now I'm finding it more difficult to write the main event. I like to be descriptive, so I enjoy trying to come up with different ways to write and describe a spanking. Most of my writing tends to revolved around the school paddle, hand, belt, strap, and hairbrush, since those are what I personally experienced growing up. My stories also tend to be about teens, mostly girls.

When it comes to writing the actual punishment part, I almost have to wait for the muse to strike so I can write something that fits the crime and narrative.

but the set up is much more fun, I mean, the ideas there are endless. I've only come up with so many ways to describe someone's backside being turned bright red.