In encouraging players to expand their methods of tackling an adventure a DM has to invest more in the details of the campaign, players aren't going to root about for more if there isn't "more" to be discovered. One means players can expand the power and have richer play is finding out what monsters know about the dungeon/adventure area. What do the monsters know?
The structure of an adventure is certainly going to dictate what monsters know but not all adventure and dungeon write-ups are very explicit in this. Do the kobolds on level 1 know there is a dragon on level 6, do they know it's a black dragon, do they even know there is a level 6 ?
If a dungeon overview has factions and a rough hierarchy spelled out keeping track of faction knowledge and what members of different rank may know will serve the trick in some manner. If the kobolds on level 1 are part of the Crimson Tide (faction) they may indeed know The Ebon Watch employs the services of a dragon, the leader of the kobolds may be aware it's a black dragon, members of the Crimson Tide may or may not know how deep the dungeon is an perhaps none really know if their faction hasn't delved beneath level 3 or so itself. Noting the general knowledge of a faction will serve the purpose a lot of the time.
Another way to record and keep track of monster/NPC knowledge of a dungeon is with tiered knowledge pools. A Tiered Knowledge Pool (or just Knowledge Pool) isn't as pretty as a prose based explanation of faction knowledge but it can provide the opportunity for a DM to quickly note what a monster knows.
The Knowledge Pools can be categorized by faction, or areas of knowledge and then broken down by rank, intelligence, or some other relative factor.
Orc Mercenaries: Crimson Tide Faction Plans-2, Level Layout (level 1-3)-2, Crimson Tide Membership-2.
sample knowledge pools:
Crimson Tide Membership
1- Crimson tide members wear red sashes most of the time.
2- Berand the Baleful is the Leader of The Crimson Tide
3- Can identify all leaders of subcomander hand higher 95% of the time.
4- Can identify all figures of authority 90% of the time
5- Can idnetify a memebr of The Crimson Tide even without a red sash 80% of the time.
6- Can name the last 3 Leader of The Crimosn Tide (Leper Lou, followed by The Termagant, follwed by Fejj and now Berand th eBaleful).
7- Knows The Termagant is still alive and rumored to be secretly plotting to reclaim leadership of The Crimson Tide.
Level Layout (1-3):
1- Can quickly locate the main entrance and exit of level 1
2- knows the secret knock to get past the red gate on level 2
3- knows where each faction is roughly located on levels 1-3
4- knows where all the sources of water are on levels 1-3
5- knows to avoid the green slimes in an about room 32 on level 2.
6- aware of rumors of ghouls on level 3
7- knows of all entrances from surface to level 1 to 3.
8- knows where the 3 most valuable treasures on the level are located.
I'll admit it I like the Knowledge pool layout (you can tell by how much I wrote about it) as it allows for a quick listing of information and in brief notation in monster writeup with a modest amount of specifics if the monster/npc knowledge pools are extensive enough.
A knowledge pool doesn't need to have all the detail of dungeon written up and simply adding a tiny bit of relative information about what a monster knows about it's neighbors will build up reasons for players to question before slaying.
12 Orc Mercanaries: HD 1; HP (6 each) AC 6 ; Atk spear (1d6) or scimitar (1d8); Move 9; Save 17; AL C; CL/XP 1/15. Knowledge: Crimson Tide Faction Plans-2, Level Layout (level 1-3)-2, Crimson Tide Membership-2. The Orcs are on good terms with the Ogre Twins in room 15. One Orc wants to trick his captain into getting bitten by Giant Spider that hunts the NW sector of level 2.
The previous has ta standard monster stat-block, goes into knowledge of dungeon at large with knowldge pools and gives some extra tidbits to offer a wider range of actions and reactions that can be built off of. If the Players bribed The Ogre Twins last session the Orcs might know this and react accordingly. The write-up doesn't say which orc wants to trick the captain just mentions there is one of them that want to do so allowing the DM to spring this on the players based on how they interact with the orcs, if one is taken captive it just might be this orc and the knowledge of the Giant Spider might be used to escape or trick the PCs or the info can be used when restocking the dungeon later. Just a few extra notes can add an awful lot to what the players will be able to learn from the monsters.