I am going to share my ideas on gaming, from various systems over many years. While it does not directly address the OP's question per se. I think it might be helpful.
Meta gaming is a reality of the process, how you handle it should be part of your gaming philosophy and you players should have a basic understanding of your philosophy. Here are some of the ways I approach gaming.
The cardinal rule that can never be broken is have fun. That does not mean no disagreements or unpleasant things happen. At the end of the session everyone should leave smiling and wanting more.
Almost as important as the first. You are telling a story (really that is all you are doing) with lots of input from your players. All of the elements of a good story of book need to be there.
I customize everything to some degree (usually a lot) to fit the feel of the story being told. Trolls, don't have to be susceptible to to fire, or regenerate, etc. This mitigates player knowledge and meta gaming based on it. In my experience players generally find this to be a good thing after they get over the initial surprise.
Meta gaming that is small in scale, reasonable for the situation, and does not break the plot should be overlooked unless it gets out of control.
No character should ever die because of good role playing. Its fantasy, if a character chooses sure death to save the party, or achieve some gravely important goal throw them a bone. Heroic fiction, daring doo and all that.
The characters of Stupid, selfish, greedy, etc, players suffer and can die, even if they never take any risks at all. This applies to the excesses that disrupt the story or group's enjoyment, not good role playing.
Mechanics wise, for every action, decision, and often die roll the players make I roll a private modification. (I roll a lot of dice when I play) This allows me to account for external or unknown (to the players) forces that might affect the outcome of an action.
This keeps the players on their toes, because their die roll may not always be the final answer. They could have performed an action perfectly but because of an unknown it had no chance of success. And most importantly it allows me to guide the story in the correct direction when it needs a nudge.
I hope this has been helpful.
To add a bit more for the OP. First and foremost the role player should role play. They should do their best to live the character, even if it means doing something that the player knows will not work. They then have the opportunity to learn in character from their mistakes and grow as a person (character). See point 5.
I touched on player knowledge and customizing aspects of your story in point 3. I noted some other answers kind of said the same thing. There was a reference to an ice troll in one answer. Take this concept up a notch. Consider the monster Manual or rule book of your choice to be a book of lore rather than law. What the player (thinks he) knows is actually the lore that the character knows from fairy tales, stories, and legends. This will make the meta gaming to role playing transition easier for the player to live with and eventually enjoyable. This will also teach players to not meta game without you always having to spank them on the hand with a ruler as a GM. They will also come to enjoy your creative license.