maddman75 said:
One method I've found useful is to drop many hooks, and see what the PCs will bite on. Maybe you have several possibilities in your home city - corruption in the guard, a looming war with a neighbor, a new theif guild rising to power, and a cult of demon worshippers setting up shop. Let them hear something about each of them and go with that.
Another important thing to remember is not to set up enemies to be defeated, but conflicts to be resolved. This requires more thinking on your feet than location based gaming, but can be much more rewarding. Determine who the players are, what they want, and what they will do to get it. Then throw the PCs in the middle and see what happens.
I highly recommend abandoning the CR/ECL/XP system for this kind of game. While it works well for 'kill em all and take their stuff' kinds of gaming, I find it lacking for a more story or investigative style of game. Personally I just hand out XP so everyone will advance at the rate I want them to advance.
maddman75 offers some great advice here- heed all of it. I really enjoy running investigative dark fantasy type games- very similar in feel to the IK stuff (except for steamjacks), and over the years I've gotten pretty good at it. My main advice would be:
1. Set up situations, not adventures. Have several plot hooks ready, knowing who the major players are, what their motives are, and how they are planning on achieving their goals. Present the hooks to the players, and let them decide which ones they want to follow up on and pursue. Once the players decide on a hook, flesh it out in more detail, and give some thought to how the NPCs would react to someone screwing with their plans.
2. Pacing. This one is really important. Sometimes players will get stymied and frustrated in an invesitigation, and thats when its time to give them a gentle nudge, but be subtle- let them think they figured it out. Maybe present them with a street urchin who tries to pick one of their pockets, and when the PCs catch him, have him offer to tell them a secret if they'll let him go- and his secret provides them another clue into the mystery. Players have a greater sense of accomplishment thinking they figured something complex out than if you present them an obvious clue. Conversely, if the players have a "Eureka!" moment and figure things out quickly- don't change things. Their insight should be rewarded.
3. Have consequences for PC actions. NPCs in investigative type games are not static, and they do not wait in a dungeon room with their treasure waiting to be slaughtered. If the PCs start asking around about them, or cause a scene or scuffle with some minions, you can bet the NPCs involved will take steps to learn more about these interlopers, and deal with them if they are dangerous. Investigative type games rely on logical consequnces to work well, and this is going to mean you need to be able to ad lib plot and NPC actions to a much greater degree than you would in a normal game. The bad news is that this is kinda difficult. The good news is that its easy to get better with practice, and its a lot of fun once you are good.
4. Don't ever say "you check the chest and there are no traps." Investigative type games rely on some uncertainty, so instead say "you don't find any traps on the chest." Things are not always as they seem in these types of games- allies can double-cross you, and the enemy of my enemy can be my friend. Play this to the hilt- your players will thank you.
5. Try not to let situations be resolved with a massive combat or firefight every time. While it can be fun, it does kill the theme and mood of the game. Instead, let the players outwit and cripple an enemy's operation that they can't kill- for example the PCs destroy the alchemical distilling operation the son of a local noble is using to produce a drug to addict the population. Killing a noble isn't an option (at least not without SERIOUS consequences), but getting rid of his illicit business might be.
6. Finally, and I can't stress this enough, DON'T use the CR/EL/XP system for giving out XP. Killing enemies to gain XP is the bane of an investigative campaign. Just decide how many sessions it will take for the PCs to level up, and go with that. Reward good roleplaying and problem-solving in this type of game, not bravado and combat prowess.