I can't point to any real resources apart from other gaming books where I would say the best advice is to look at as many styles and approaches as possible. I've tended to pull ideas from a variety but in general if there is an established style for the system I'm writing for I try and emulate that.
I pretty much always work solo. It's not ideal but as an indie publisher who isn't really earning anything (across everything I've solo published I've made <$50 to date) I can't justify paying somebody to collaborate on or edit my work. The couple of times I've had an editor (one paid gig, one piece where a friend playtested/edited) it has made a massive difference and I'd love to be in a position to get somebody to do so again.
Having to self edit the best trick I've learned is to get the first draft finished and then walk away from it for a couple of weeks. That helps clear my mind and means I have to reread text properly rather than relying on my memory of what I wanted to write.
As for surprises in organising - no, not really. For writing I tend to use Google docs solely because it is usable on my phone. For the first draft I keep sections as separate documents and then merge them all later. My largest RPG piece so far is about 10,000 words (a series of missions for The Sprawl RPG) and for that it has really helped having a format that had already been established. So I had all my section titles, order etc and knew roughly what size each of them needed to be.