Hi there, my advice would be to define a precise game design document. Then it should be possible to make the graphics and the develop the game simultaneously. Furthermore you need a task managament tool, where you define all the task, who should do them, and the progress. https://trello.com/ is one such tool, and its for free. I also advise you to have all the communication centralised, so either in the task management tool, or in something like a forum. If the communication is spread over several e-mails it will be difficult to keep track of all that was said. Finally its important to define deadlines for each task, or the project will enver effectively go forward. Hope that is helpful, have fun making games! Thomas