If the experience of Deus Ex taught me one thing, it's the importance of team dynamics. You have to build a team of people who want to be making the game you're making. You have to deal with personnel issues sooner rather than later. And there has to be a clear chain of command. Many decisions can be made by consensus, but there can only be one boss for a project, there can only be one boss for each department, and department heads have to answer to the person heading up the project.
Clear goals are great .
We started out thinking very big. A really big budget, no external time constraints, and a marketing budget bigger than any of us had ever had before made us soft. For one, there's no way, in a first-person RPG, to stage a raid on a POW camp to free 2,000 captives. Also, there's no way to re-create all of downtown Austin, Texas, with any degree of accuracy. Third, blinded by the power of UnrealScript, many of our original mission concepts depended upon special-case scripting and lots of it.