I barely ever read game previews, or even keep up with information about games I am interested in purchasing. I might read the occasional developer interview or keep up with information about the game if the news comes directly from the developer, but external sources previewing a game typically does not interest me much.
I learned my lesson in trusting game reviews after reading IGN's poor review of ZombiU. It nearly caused me to return the game, but I decided that I was going to play it since I already bought it to come to a decision for myself. The game was thoroughly enjoyable for what it was, and I'm glad I didn't listen to the negative reviews. Reviews are usually one man's (or woman's) opinion; opinions which may or may not reflect your own.
I guess I basically just trust my instincts on a game. If I like what I see and think it'll be a good game, I'll probably buy it. Sometimes my instincts are wrong and I'll wish I'd have listened to the negative feedback instead, but that's just the way it goes I suppose.