Whether you're a plotter or a panster by nature, gamebooks do need that extra input to keep everything in line.
I find that a mixture of tactics is needed though - you'll probably need to switch strategies to suit all the different aspects that are part and parcel of writing a gamebook.
So, what are the options?
1. Floor plans, illustrations and creating atmosphere. This is one of the first things that I start sketching simply because I think it's crucial to get in the zone. Floor plans can help you to visualise your location and, if you can picture yourself walking along passageways, into rooms, through forests and over rivers, then you can better describe it. That matters, because you want the readers to be able to imagine themselves in this place too. If they can 'see' where they're heading or what they're facing, they're more likely to be engaged in the story and the decisions. So far, I've used real places that I know well but using drawings or photos of places that you'd like to set your story in would work equally well for this purpose.
2. Flowcharts, flash cards and ordering information. At the midpoint of Nightshift, the reader needs to find the exit. Prior to that they need to find the entity who knows where the exit is; discover where this entity is; learn how to communicate with them and find the object needed to gain the information. So I had to make sure that all of this was available beforehand. It's no point having the reader arrive somewhere missing an essential clue. Well, they might be missing it because they chose a different route, but it should have been available to find! I think flowcharts are an excellent tactic for clarifying all of this. They helped me to check, that I hadn't missed any steps out and were also useful in inspiring further events or side games. For example, if you plotted that the reader needs to find a book, seeing that written in black and white could strike you as being too easy, so you may decide to squeeze in an extra layer of deciphering. Shift your flashcards around and Bob's your uncle!
3. Branching diagrams and ensuring reference mapping works. These are invaluable for making sure that you haven't forgotten pathways and that the routes do follow on methodically. I absolutely needed them for the endgame in Nightshift, where there are different variables in play. If you had a certain number of factors wrong, it wasn't a good ending for the reader, while all correct got them the magic 'turn to 400'. Something in between, ended in yet another consequence. To track all of those was a logistical nightmare but branching diagrams ensured that I led the reader to the right place and not to confusing paragraphs that made no sense or were missing information.
On reflection, these are all quite visual plotting strategies - I guess that's just how my brain works. I tend to spread flash cards and huge maps out over my table and then it comes together for me. Naturally, each gamebook writer finds their own method which works for them, but if you're currently struggling, maybe give one of these a whirl and see if it clicks.
I'm really interested in other plotting strategies that gamebook writers swear by - I'd love to hear about them and would like to feature them in a follow-up post too. If that's something you're interested in, please get in touch.