The working process. The more the people involved interact with each other, the better the results will be, faster and of better quality. Even if you all work from home, get together frequently and discuss how far you’ve gone, what comes next, delegate your tasks, set deadlines. Make a summary of your meetings, and add it to the plan you are following. Record as many things as you can - so you'll have an updated plan and you will be able to follow the past steps and in the case of a second project to smooth out some of them.
It is impossible to describe everything that accompanies such a complex creative process, as is the creation of a game. I hope the general guidelines I have laid down prove useful to you. Good luck!