I was just chatting about this topic with some friends. Heh.
My games tend to be very popular. I'm slowly learning why... I'm often pissed with my poor preparation, and how wild and chaotic the games get, but I think I know why.
This is what works for me:
Let the PCs win. No, I don't mean hand them everything on a platter. But if they do something smart and proceed, they should get _some_ positive result. Maybe not the one they wanted, maybe not a complete success, but something.
A game where players feel like they loose in most or all situations will rapidly build a sense of conflict between players and GM. Dark games, where people are tormented in various ways, aren't necessarily games where the players loose. Some players quite enjoy backstabbing one another or acting out the suffering of their characters. The key here is finding what goals the players have, and meeting them.
If the players come up with an idea or plan, _facilitate it_. Nothing is more frustrating than coming up with a brilliant plan, and then having it simply get waved aside. If the players have a lot of fun doing something, give them something for it. Reward it. This is what is getting the people involved.
I was in a game where my character was on trial. The players conferred and came up with elaborate plans to defend me. One PC engaged in this wonderful monologue about the situation. We pulled political strings.
Turns out that due to politics, it was a show trial only, and I was freed. We were so incredibly pissed that it turned out _nothing_ we had done made a




load of difference. What did that teach us? Not to bother.
Powerful NPCs. If powerful NPCs are solving the PCs' problems, kick yourself in the ding. Now twice more, for good measure.
This is different than politics or quests. A quest to get a god to save your city from plague, or to destroy an uberpowerful demon, that's cool. Fighting an uberpowerful demon, getting your ass stomped, and having your page turn out to be an avatar who's been manipulating your party, that sucks.
Again, it's about the players being _involved_. Being spearcarriers for your NPCs is no friggin fun.
Anything the players don't know is fair game for change. Rewrite the entire history, if it becomes necessary (though it rarely is). Like a previous poster said, if you have a hermit who knows about lizardmen and they don't go for it, add characters who do.
What they know is not what you know. Players have a marvellous ability to ignore the most 'obvious' of hints and clues about a game. I've been on both sides of this. If it's clear they're not getting it, and they _should_, give them more hints. True, there's only so far you can go with this and still maintain some sense of freedom, but if a player has his character do something the character should know is breathtakingly stupid, let the player know. If they then insist, well, fine.
Often this is because of information lurking in the bottom of the GM's mind. It's easy for communication to bog down, particularly in combat (one plus with D20's encouragement of mapping things).
For example, in one game I ran, the party had armed gunman facing them, and a treeline a distance away. The gunman had just popped out of a helicopter. One player said "I break for the trees." Now, in my mind, this was amazingly dumb. No _way_ the person can get to the trees without being blown full of holes! I asked him if he was sure, frowning a bit, and he affirmed. Then was pissed off when he promptly got shot a bunch.
Turns out we had _very_ different mental pictures of how ready the gunman were, and where that treeline was. Oops! This was completely a matter of communication.
Some GMs would have simply said 'he should have made sure', or otherwise asked me about the situation. Maybe. Maybe I should have been more informative, or mapped it out.
Even if you decided it was the player's fault, is it fair to blow his character away?
Some people may enjoy the dissection of events, and the everpresent danger if ones attention wavers for a moment. Personally, I don't.
Anyhow, that's what works for me and the people I've known.