The correct terminology is "partial marshal" ;-)
I go for what makes sense. One of my groups has a player who doesn't pay attention to what's drawn on the map. He'll walk over walls and off piers because he claims he can't see the marker. It doesn't make sense that his character would go for a swim mid-combat, so we remind him that the pier ended 3 squares ago.
That said, I'll only remind someone of the same fact so many times. If the players haven't figured out that they need to headshot zombies in Deadlands after five combats, that's their own problem.
My plots proceed on their own. If the NPC who wanted to hire the PCs fails to do so, he'll hire someone else instead. Maybe the PCs will notice.
I never run a single plot thread at a time though. It's okay if the players ignore half the plots. I also have so many plots going that at least one of them will be able to interrupt the PCs and prompt them for attention if needed.
Leveling happens outside of game. I try to make loot division happen there too, but haven't been successful at that. Last game I had a couple players who didn't like email and they ended up bogging down email based loot distribution to the point where it wasn't worth the trouble.
I try to be available to answer questions. I don't pretend to have the highest level of system mastery at the table. In D&D 4e, I fully expect every player to know his own class better than I do.
I want my players to surprise me with their creativity. I will never outright shut down a creative idea.
One mistake I've seen other GMs make is that if they don't think an idea will work, they tell the players. A few games ago, I got told I couldn't cast an illusion on some wooden discs to make them look like gold coins because the weight would be wrong. That's a perfectly legit reason for the ruse to fail, but the GM shut me down before I could even attempt it. The correct response would be to let me cast the spell, maybe give me a perception check to notice what was off about the coins, and then let the NPCs react to being given wooden coins.
I also like it when players come up with legit, working solutions that I never saw coming. I'll happily let them bypass a few sessions worth of my prep work. They feel awesome when they do. If their solution causes the game to deviate so far from what I expected that I can't recover, I'll even go so far as to ask them for help coming up with ways to get back to where I need to be. Outsourcing narrative work to your players will make them feel like contributors to the story instead of just an audience.
I don't do modules, so I can't comment on that. For Deadlands, I don't think there's anything wrong with having the occasional comic relief module.