The job every GM faces is to immerse the players in the make-believe world of your setting. You can do that in lots of different ways, but in an article I posted at MCG titled Breathing Life Into Your Encounter, I focus on a few strategies for bringing a specific scene to life for your players.
For example, I stress how when your player characters enter an encounter, don’t hide what’s important about the encounter behind less-important minutia. For example, if PCs exploring a ruined cathedral enter a chamber containing a two-headed wolf sleeping in the nave, lead with the wolf. Don’t start out describing the room’s dimensions and the number of windows. Those details can come afterward.
More? Check it out the entire article here, which lays it out in "5 Easy Steps" :).