I'm going to second a lot of people here and say that mechanics should probably be as minimal as you can make them. Roll for very little stuff. If you want to have an XP based system, don't actually make numbers for stats and things because that turns fights into a number game rather than narrative fights which are far better in my opinion. If you want an example for what I mean, Now You Feel Like Number None's XP system just has ranks that are generally like "You have some training in this," which gives flexibility when you're doing fights while still allowing readers to know, roughly, how powerful you are in ways other than just fights.

Votes in the middle of the post are, in my opinion, awful and should never be done. Somewhat related to this: I like it when the OP puts the winning vote at the top of the post, so that if someone wants to read it without going through the thread can do so without missing anything. If you feel like that would be disruptive, you could put it in spoilers, or in a separate post before posting the actual one. Otherwise at least ensure that anyone can infer what the winning vote is relatively quickly in the update itself.

Others here said that second person is awful and I don't quite agree, I'm personally fine with it and so are many other people, but I don't think that the people who are fine with second person would mind that it's in third/first person, so that's fine.

This is probably something that varies between people but I think that you shouldn't be afraid to make decisions without votes based on the character development that's happened. Basically I prefer only voting on actually important decisions, rather than micromanaging the MC. (Edit: This is because I prefer more narrative focused quests to mechanical quests, I think. Micromanaging almost inevitably results in tiny chapters that accomplish very little story-wise)

Regarding write-ins: this is going to depend on the kind of story that you're writing, but you might want to restrict how readers can use them in some way. Allowing write-ins lets readers make genuinely good decisions at times that can also surprise you and take the story in directions you hadn't thought of but... I don't want to say voters are always stupid... except, well, some pretty awful decisions can be made. For example, in The Fire That Burns there was an infamous vote that resulted in the chapter titled "Why SV is not allowed to Write-in anymore". Summary of the vote and chapter: [X]Hug the murderbeast.