Preparation is among the most valuable tools at the disposal of a good dungeon master. It can help at every level of the game—encounters, both random and planned, quick reference to NPCs, pivotal plot points, and overall cohesion. There are times, though, when it is possible to over prepare, to the point where it can become an active detriment to your game.
Overpreparation is a fairly common pitfall for novice dungeon masters, though sadly not exclusive to them. It can occur when the DM wishes to present a smooth experience, or when he or she has a vision of an epic storyline in mind and wants to ensure that the players get to experience it just as it was initially imagined. The players are herded along, often more by stick than carrot, and sometimes even accompanied by a DM-controlled member of the party who will ensure that they stay on track by varying degrees of forcefulness—essentially a parole officer to make sure the players don’t get “lost” along the way to the next plot point.
This kind of DMing behavior is colloquially known as “railroading”, since the players are essentially on a fixed path from point A to point B without any chance of meaningful diversion from that path—much like a train cannot run where there are no rails. In short it negates the role of the players in the story and relegates them to being passive spectators to the DM’s vision of the plot. While there is nothing wrong with telling a story, the idea at the core of a roleplaying game is that everyone gets a chance to participate, and railroading diminishes or removes the ability of the players to do so.
One difficulty in avoiding railroading your players is that many of the techniques and intentions that lead to the adventure being “on rails” are simply misapplications of perfectly valid methods of DMing a game. It is entirely possible to have a DMPC who does not overshadow or direct the players, for example, or to have a grand and epic plot for your campaign without cutting out your players ability to meaningfully contribute to the outcome.
The main trick is to remember not to become overly involved in your preparations, or to prepare so thoroughly that you lose the flexibility to adapt to new ideas. The 4th Edition Dungeon Master’s Guide advises saying “yes” to your players as much as possible, or at worst “yes, but”, rather than saying “no.” This is very good advice to keep in mind, within limits—sometimes you will want or need to say “no” for the good of your game. If you are inclined to say no, though, pause for a moment and determine why that’s your immediate reaction—and if it’s simply a knee-jerk response, you may want to change it to a conditional yes.
Another thing to avoid is lengthy periods of description or dialogue where the players are left listening to you talk. In many ways, a good DM talks as little as possible at the table, leaving the players in control. This advice is often difficult to grasp for novices, especially when working from pre-written adventures, since there is a tendency in those to run a paragraph or two of scene-setting flavor text. It can be very evocative to have such description, but again remember that the role of storyteller is only a part of the DM’s job, and is secondary to ensuring that your players are having fun. If your group loves the descriptions as you set the scene by all means, be as flowery as you like, but keep an eye on their body language. If on the other hand their attention begins to wander when your narrations run past a few sentences, keep the descriptions functional and brief, detailing only what they need to understand directly to function. If they want to know more, they will ask, and that’s when it’s generally better to describe in more detail.
The DMPC is a touchy issue. Some groups are more accepting than others of these characters, but there’s always the possibility that the DMPC will be viewed as a babysitter or warden, regardless of your intentions with the character. In general it’s easiest to avoid using them altogether, neatly sidestepping the problem. If you do decide to have an NPC accompany your group, consider making him or her a noncombatant or placing control in combat into the hands of one of the PCs and letting them run the character as a companion. No matter what, make certain that any advice or directions given by the character are suggestions at best, and that they will never overshadow the PCs role as the stars of the campaign. There is little more frustrating for a player than to fight against a seemingly impossible battle only to have an NPC appear to save the day through DM fiat.
Above all, remain flexible and remember that everyone makes mistakes. If your campaign begins a little rough, that’s fine—better to be rough than to be too restrictive. By the same token, it’s never too late to relinquish some of the control back to the players, if you HAVE been railroading. And the ultimate truth of gaming—as long as you’re having fun, you’re doing all right—still stands. If your group is satisfied with your game, don’t fret too much that you’re railroading them. Don’t assume, though, that simply because nobody is complaining it means nobody is unhappy. As I have repeated many times, communication with your players is key to making sure everyone is satisfied.