This is another time where it seems appropriate to say it: There is no such thing as metagaming, outside of inventing it as a thing that must be done in order to "avoid metagaming." There is only playing the game in good faith, and playing the game not in good faith.
To elaborate, because I'm sure the statement thus far has made at least a few people think I am out of my mind, and a few others confused:
If a player takes a course of action in the game that any brand new player with zero knowledge of the game could also choose to take, then that course of action must be okay for them to take - saying that it isn't because they know out-of-character that it is a good course of action to take is forcing the player to utilize their out-of-character knowledge to determine their character's actions, which is the exact thing that is being claimed to be avoided. If a player says "let's go left" it doesn't at all matter if that was decided by whim, coin-toss, or the player knowing that if the party goes left first they'll reach a treasure of some kind that will help against the more difficult encounters faced when they go right - those are all perfectly fine and not metagaming because they don't rely on the player knowing something the character doesn't, as the character is just picking a direction.
It is only when a player acts in a way that a brand new, unknowledgeable player could not possibly choose to act that there is any issue - and even then it isn't one of the utilization of knowledge that is out-of-character that is the problem, it is knowing the impossible.
The separation is simple: anything a character might possibly know or guess at is okay to act on, regardless of player knowledge since the use of player knowledge is what is supposedly being avoided in the first place; anything a character couldn't possibly know and couldn't possibly guess at is off limits, regardless of player knowledge since that is, again, what is supposedly being avoided.
And to really blur the lines: even if a player says something that their character couldn't possibly know, such as "let's buy some silver weapons, there are lycanthropes later in this adventure," that isn't actually metagaming because the character doesn't actually need to know for sure that there are going to be lycanthropes in order to buy a silver weapon, and is, in-character, buying one "just in case." And again, the new player that doesn't know anything test shows that this can't be metagaming because they could choose to shop, and then choose to buy silver weapons with no more knowledge of their significance than that they exist and can be afforded by their character.
