“It's a cliché, but it's also an important rule of narration: “Show, don't tell.” Imagine how the environment would look and sound in a good movie, do your best to describe it that way, then add details of smells and texture that a movie can't communicate. Don't tell the players that there's a pool of bubbling acid nearby, show it to them with a vivid description. Think about how acid might smell, talk about a cloud of noxious vapor hovering above the pool, and describe what the pool bubbling sounds like.
Your Only Limit Is Your Imagination: Your imagination is the only boundary in your description. You aren't limited by a special effects budget. Describe amazing vistas, terrifying monsters, dastardly villains, and bone-crunching fight scenes. Your enthusiasm and liveliness are contagious, and they energize the whole game.
Portraying Rules Situations: It's easy to fall into the rut of describing events merely in terms of the applicable rules. Although it's important that the players understand what's going on in such terms, the D&D game can be at its dullest if everyone talks in “gamespeak.” You know you've fallen into this trap when the table chatter is: “That's 26 against AC,” “You hit, now roll damage,” “31 points,” and “Now we're to initiative count 13.”
Instead, use such statistics, along with your knowledge of the scene, to help your narration.”
4E DMG.