From Module B1: In Search of the Unknown:
First, it is crucial to keep in mind that this is a game based on player interaction and player choice. The game generally follows the course of the player's actions—if not always their plans! As moderator, you present an ever-changing situation as it occurs (sort of like an unfolding story, or even a movie, if you like to think in those terms), and the players respond pretty much as they desire. As the game goes on, you are presenting them with a hundred different opportunities and choices—exactly how the game goes will depend upon their response to those opportunities and choices. For instance, if players decide to walk down a corridor and find a dead end with three doors, they have a number of choices—simply turn around and ignore the doors, listen at one or more before proceeding elsewhere, try to open one or more (either normally, by forcing them, or even by simply bashing them in), or whatever. You describe the situation, then await their decision as to a course of action. Of course, some decisions will be more difficult, or quick, or crucial to survival—and as always, imagination and resourcefulness, as well as quick thinking, will usually be rewarded.
Second, a good DM remains "above the battle" and does not attempt to influence player actions or channel the activity in a particular direction. The Dungeon Master should do everything possible to assist players in their quest without actually providing important information unless the players themselves discover it or put the pieces of a puzzling problem together through deduction or questioning, or a combination of the two.
A large part of the game consists of player questions, many of which are, "What do we see?" Your job as gamemaster is to answer those questions without giving too much away. You need not hint to players any information that they do not ask for on their own, except in unusual instances. Allow them to ask the questions, and allow them to
make the choices.
In the same vein, as Dungeon Master you will enjoy watching players wrestle with the problems you present them with. Although you may set up situations to challenge them, you must understand that you are not their adversary, nor are you necessarily out to "defeat" them. You will enjoy moderating a well-played game where players respond to the challenges encountered much more than one where the adventurers foolishly meet their demise in quick time. However, if your players abandon caution or make stupid mistakes, let them pay the price—but be fair. In many cases, a danger due to lack of caution can be overcome, or a mistake in judgment countered by quick thinking and resourcefulness, but let your players do the thinking and the doing.