wedgeski
Adventurer
This problem can be taken to an extreme with multiple PC's, all roleplaying their characters different and effectively, trying to avoid metagaming, in an investigative campaign heavy with innuendo and clue-dropping. 
The way I deal with the problem? Session journals. If you take the time to write up the details of the last session, you can often repeat the subtler clues, and otherwise generally steer the reader - i.e. your players - in the 'right' direction. Obviously, though, you shouldn't be writing a work of fiction, so the journal *must* accurately reflect what went on.
Sometimes a clue just doesn't come out right, or the players are distracted by another priority, or they have no in-game reason to believe anything they're told by that NPC, or whatever. When they come to read the journal, they may have a clearer head and see something they missed.
Plus you get to stretch your writing muscles and create a good record of the campaign in the process.

The way I deal with the problem? Session journals. If you take the time to write up the details of the last session, you can often repeat the subtler clues, and otherwise generally steer the reader - i.e. your players - in the 'right' direction. Obviously, though, you shouldn't be writing a work of fiction, so the journal *must* accurately reflect what went on.
Sometimes a clue just doesn't come out right, or the players are distracted by another priority, or they have no in-game reason to believe anything they're told by that NPC, or whatever. When they come to read the journal, they may have a clearer head and see something they missed.
Plus you get to stretch your writing muscles and create a good record of the campaign in the process.
