The NaNoWriMo novel writing project hasn't imposed too many restrictions on me (other than having to find two hours a day to work on it). But there is one weird constraint: I can't read any other fiction while I'm working on it.
That isn't an official NaNoWriMo requirement: it's just a reflection of my fear that if I read something particularly striking, that will end up influencing what I write. That was particularly a worry early in the month, where I was writing plenty but the style was a tad fluid. I'm relatively confident know about which style I need, but I still don't fancy being distracted (or disenheartened) by something entirely different.
That might be different if I was working in a well-defined genre, though even there the risk of conscious or sub-conscious plagiarism might dissuade me. Do you like to cut off other influences when working on large creative projects, or do they fuel your activity? Share your approach in the comments.