I know this is kinda late but... better late than never, right?
Arch mentioned that I've used pre-written campaign modules... It's true I have used them often. They're a great way for a new DM to get a sense for how the story should be structured, what kinds of combat challenges should be presented to the players, etc. I'd urge any new DM to try at least one to get a feel for how things flow.
I continue to use them because they save me time. Unless I have an inspiration for a really good story idea, I prefer to use modules to keep things going.
Right now, I'm running Hoard of the Dragon Queen for my local gaming club. It's a very long module, meant to be played as a full fledged campaign. It's our first foray into the new 5th Edition and, like I said above, it's helped me to get used to gauging the proper level of challenge for the party with the new rules. It's a pretty good story, and the players are enjoying it a lot.
"He who takes offense when no offense is intended is a fool, and he who takes offense when offense is intended is a greater fool."
"Don't take refuge in the false security of consensus."