The more organized you are, the easier it is going to be on you, period. There is another factor to consider also; when you have your notes behind the screen and the players can’t see you flipping through the pages of the various monster manuals and such, the suspense and mystery are present by virtue of the players’ not knowing what’s happening. If they can see what books you have open and you are flipping through the pages looking for information, several things happen. First, the game is slowed because of the hunt for information, second, the suspense is eliminated or greatly reduced because they can see the books through which you page, and third, you end up looking like you don’t know what you’re doing, even if you have every last minutia planned out to the nth degree. So here’s how you organize yourself...
1. List everything you will be needing. NPC’s, monsters, treasures, plot points, locations, everything should be listed.
2. Sort through the list and arrange everything in chronological order, geographical order, and in order of importance. List locations, followed by the population of the locations, and the “things” that are found in those locations. If it’s a dungeon, for example, each room, hallway, trap, treasure, etc. that is there, write it down in as much detail as you need to let you know what is there so you can describe it accurately. If it’s another type of setting, note everything you can think of that is of importance to the story at hand and remember that the less you refer to the books, the more effective and efficient your game will run.
3. Pre-roll major plot points. This is a tricky one because there are so many x-factors involved, BUT, if there is a major point that will happen that the players will witness, or may witness, then if it is already played out, then more time can be spent in description and orchestration than DM die rolling.
If it is a prefab or published adventure, then it is already delineated and all you are required to do is to read it THOROUGHLY. Make sure you know it inside and out before starting the game and you’ll be light years ahead.