Identifying the issue (creep) is the first step. If you had not yet done so, there is this wonderful thread to read on just this topic:
This really is a design question you are wrangling with. Many authors here take different approaches to deal with this – @hustlertwo’s circle idea is one. I would also suggest using a flow chart to chart out your game’s path.
With flow-charting you can visualize, where each decision is, where each branch occurs and how you bring everything back into the trunk of the game. There is a free program I use: yEd Graph Editor, and it is a real gem.
There are other tools authors of this community use as well. I would look at the following thread for some ideas and options:
There are no “right answers” for every project – for example, even though I am using the flow-chart system for my major individual project, such a method would not work in a collaboration project. So, with the collaboration project, we are using the old-fashioned game “piece-meal” approach.
We design each “level” of the game as a group, come to a concensious(sp) and then break the levell down into parts that each collaborator then works on. The key to succeeding here is communication. The more you have of it with those you work with, the better you are.
I am very fortunate to have found people that sometimes seem inside my head for this project (it is amazing how we are always on the same wave-length) yet, even with such amazing and experienced people I am working with, we still talk every day we work on the project.
Hope all this helps.
Edit: Here are some general help links as well.