Hmmm... okay, tips for new DM's.
1. Own Far Too Many Dice to be Logical
That's a good start.
listen, as a DM, you will need every single die in your toolkit at one point or another. I've had DM's who brought model trees and columns and miniatures of every available kind to the battlefield, but never one who could set the scene so well as the player who puts down three d6 stacked high and declares "this is a column, and these single d6's make a wall... with high, narrow windows here, here.. and here."
the surplus of dice is your friend. Nothing makes you look less professional then asking for someone to loan you their dice, and certain spells and effects require lots more dice than you get in your basic boxed set.
2. Railroads never end well
You may think that you have control over your players, but if you put too much stress on them, the train will jump the tracks. you'll either be left with no players or a colossal mess of a campaign. nobody wants towork with either.
3. Let the players argue with you.
sure, you could just use ample application of rule zero, but why bother? you have four, living, breathing people there who are willing to look up any rules you might be shaky on. if a player contests anything you do, don't immediately smack him down, give him a chance to explain his position. If the rules say he's right, he may very well be right, and it'll improve your standing in their eyes if you conceed that, even as a DM, you are human.
4. Know when to put your foot down
If you think a player is doing something shady, put your foot down. Read their character sheets. Check their math. Add up their feats, make sure they qualify for everything they have, and have only things you've let them have. Make sure their stats haven't been drifiting upwards since level 1. Make it known that you have to give prior approval before all spells / classes / prestieges from splatbooks / 3rd party sources / pdf files are allowed in your game. If you do it politely, this isn't an invasion of their privacy, or disrespectful to them in any way. Just let them know that in this world, you are the one who decides what goes on.