As a GM, I don't need to make metagaming a problem, so I don't. You can read the MM, have it open in front of you, and it's not going to change the level of difficulty in the encounter or help you much get done what you need to get done. Once I started designing encounters with the assumption that players will know things, it became trivially easy to avoid having metagaming be any kind of problem. And my games do not resemble the players trying to win at all -- largely because just knowing things doesn't really help all that much.