Well, both DMG1 and DMG2 have some good advice on the subject.
There are various things that should be considered when narrating, and different considerations may apply in different situations to some extent.
One thing that is easy to run into is the situation where the DM knows many things but they aren't all communicated effectively to the players. Say you are drawing out an encounter area on the battle mat. Make sure the player's understand what everything is. It is most fun if you describe it in colorful terms as the characters would see it, but don't be afraid to make some comments about possible mechanics either. Usually you can couch those in descriptive terms as well, but don't be too vague, and be prepared to clarify if it seems like a player may not have caught onto something that would be apparent to the character. For example if a player decides to have his character run across a rickety bridge make sure he understands that the bridge is dangerous and outline what the mechanical implementation of that is, like: "OK, Carlos can see that it is possible to cross the rickety bridge, but it is swaying and the ropes appear to be very old and there are missing or rotted slats in the decking. You're going to have to make an Acrobatics check with DC15 to run across, or you can make it DC9 if you move at half speed."
When the PCs are in a non-combat type exploration situation things are similar. In those cases you probably want to focus more on clues and atmosphere. "The air is heavy, warm, and moist in this passage and the walls are rough natural rock. You can see what appear to be claw or tool marks indicating where the passage has been widened in places. Ahead there are two branches. One plunges steeply downward and to the left, the other is much narrower and goes to the right, but you can detect a whiff of cooler air and a faint tang like the air after a lightning storm coming from that way. Various insects can be seen scuttling underfoot and you notice a burned out torch discarded by the junction as if someone who came here before may have stopped for a time." Some atmosphere, some clues (assuming the players have some context to interpret them), and a generally evocative description engaging multiple senses.
When dealing with NPCs give them all some minor distinctive feature. Instead of telling someone they see a Priest of Erathis "You meet Johan, the head Priest of Erathis, he looks annoyed." you can say "A middle-aged man dressed in the vestments of Erathis approaches you with heavy rapid footsteps, his fine cloak swirling behind him. You notice that his features appear pinched and he wears an expression of annoyance. He stops suddenly in front of you and says..."
I find when doing general description that the best thing to do is simply imagine the scene. Close your eyes for a second and picture it in your minds eye, and then describe that like you would describe a movie scene to someone that can't see it. Go crazy, toss in details and color. You'll find that your mind's eye will supply imagery that you wouldn't have consciously thought about. You can do that before hand and write it down too, or at least jot down a note or two.
Narrating combat moves is of course going to be a bit more improvisational. If it is a monster just RP it. Imagine you're the monster, there's the situation, you want to do X, roll whatever dice you need to roll, and describe what you imagine happened. "The huge orc leader with the great axe leaps forward, raising his axe for a mighty blow to Osrik's head! The doughty dwarf tries to step aside and make a counterstroke, but the orc's blow strikes his shoulder with a mighty clang! Osrik, you take 29 points of damage as the orc expends his Mighty Blow power."
. So if there are any good books articles tips tricks anything would be great thank you.
