Alright, so imagine you’re running a Pathfinder game. You’re party opens a door to a new area, and this happens:
You: Make a Perception check.
Player: Uh… I get 14.
You: Alright. The room is empty.
Player: But why did you make me make a perception check? There’s a trap. There must be a trap. Send the fighter first.
And… end scene.
People who DM know what I’m talking about. You need to give your players a chance to notice something (monster hiding, trap, secret door, whatever). They fail their roll so their characters don’t see anything… But now the players know that there is something they didn’t notice. Will that affect how they play? Well, it shouldn’t. In theory, that falls quite firmly into the meta-gaming category, using knowledge their characters don’t have to make character decisions… But it’s hard not to, especially for newer players.
So how do you handle it? By the rules, you need to give them the opposed check (Search, Spot, Perception, whatever it’s called in the game you’re playing) at a certain point. But you don’t want them meta-gaming. So what do you do?
All the rolls
One option: they roll all the time, whether there is something for them to find or not. They walked into a new room? Roll for perception before you describe it. If there is something for them to notice, add the appropriate descriptive elements.
The problem with this one is obvious. It takes time. It slows things down. It gets boring. Is it worth making the game slog through roll after roll to save your players from getting “too much information”? Maybe it is, for you. By all means then, do it. But, if not, you need a different option…
None of the rolls
Don’t let your players roll to find things automatically, ever. If they want a chance to see something, they have to make a conscious decision to look for it. That will make it a lot less likely for your players to actually find things, though, since they may not think to look. Or maybe it will make them paranoid, and they’ll just choose to roll all the time (see above). It also ruins the narrative idea of “catching a glimpse of something”… If a monster is trying to hide and does a crappy job (rolls a 2), does it make sense that the players need to decide to search, rather than just notice them?
Another alternative to this idea is that you, as a GM, make the rolls for them. You don’t tell them what you’re doing, you don’t tell them the results… but anytime they need to make a check to notice something, you make the roll and give them the information as necessary. It’s not a perfect system for a few reasons. It’s more work for you, for one. And, if a player really wants to meta-game, they’ll do it no matter what (“Gasp! He’s rolling again! I bet there’s a trap!”). But it gives them a *bit* less information, without completely stopping them.
…Some of the rolls?
My personal preference, for players who meta-game too heavily, is a bit of a cheat. Figure out who has the highest bonus in whatever stat or skill determines the “notice something randomly” factor (Spot in D&D, Perception in Pathfinder). Figure out what the total would be if that player rolled a 10 (or an appropriate half-way average if not rolling a d20). That’s your baseline. Now, if the party comes across anything that could be spotted with that baseline as a result, someone (whoever has the highest) notices it, no roll required. Anything higher than that baseline, they only notice it if they look for it (actively decide to search).
So let’s say I’m playing Pathfinder, and Bob the Ranger has a Perception of 15. If he rolls a 10, his result is 25. So anytime Bob comes into a room where something is hidden, if the difficulty of that hidden thing is 25 or less, Bob notices it automatically. If it’s 26 or higher, Bob won’t see it unless he decides to roll for it and gets a result higher than 10.
The advantage of this is that it keeps the “random notice” factor, without ever giving information away… Because the party is only getting information if there is a success, even if that success is an automatic, no roll required success. It also speeds the game up by eliminating rolls when you know the party is likely to succeed them.
Or, you know, just go with it.
The final option is to just play by the rules, and trust your players not to cheat. Most people (at least, most people you’ll want to play with) won’t cheat on purpose or maliciously. If you think you’re players won’t meta-game, or you think they understand the transitory nature of characters enough to not be obsessed with keeping them from all harm, just play by the rules.
If, however, your players do have a habit of meta-gaming (even if it’s only because they’re new and don’t understand how to separate player knowledge from character knowledge), try out some other techniques. See what works for you.