It is really hard, especially being on here all the time.
Trying to go into Psychonauts 2 blind... but I probably already "failed" in your eyes OP as I think I may have watched an early concept trailer or teaser trailer.
However, I've been trying to do this for pretty much all games I'm playing though, as it helps me go in unbiased. If I'm interested in a game, it shouldn't really matter what anybody else says about it. Granted I have to know SOMETHING about the game, like the overall premise of the game or I probably won't play it. So again, watching at least one SHORT teaser trailer to gauge interest. Beyond that though, I try to abstain from watching any gameplay videos, looking at reviews, etc.