I've found that, like most things, GMs can be divided into a few categories. Lousy, Fair, Good, and Great.
Being Fair is pretty easy. Keep your world consistant, don't be a jerk, and listen to your players.
Being Good is quite a bit harder. This requires you to be able to grab your player's attention and get them interested in the game. Other comments in this thread are a good start. I highly recommend
www.roleplayingtips.com
Being a Great GM, though, is a matter of both talent and experience. Others have already answered your questions on the normal level. Here's a much deeper set of answers to keep in mind, but not necessarily stress over at first.
1) Is there anything that all of you, in your numerous collective years of experience, feel that a virgin DM should know?
The whole purpose of playing a game is to have fun. I know this seems obvious, but it is actually quite easy to overlook in the middle of a game. Inter-player personality conflicts, boredom, dissatisfaction with the plot, with thier character, with their die rolling, with your descriptive style can all lead to a lack of fun on the part of a player.
As a GM, it falls to you to keep track of everything, all at once. Don't forget to keep a good eye on your players. Every couple of minutes, at breaks in the action or the flow of the session, sit back and study your players. How are they sitting? What are they looking at? What are they talking about? Who isn't saying much? Why? Being able to attend to your players' wants and moods, and adjusting the flow of the action to compensate makes a big difference in their enjoyment of the game. Ideally, they shouldn't even realize that you're doing this, but only that they're having a great time.
While consistency in your world is vital, so is attention to detail. Don't let the game world just sit there until the players interact with it. Have it come to them. Have a dog start barking at one of the PCs while they pass through town. Have a squirrel be watching in the woods. Use the weather! Snow and rain are great tools to add life to a world. Have things happen for no other reason than to add life to the world. It's the little things that make a difference. What's great is that it doesn't really take much to do this. Just a touch here and there is all you need. Minor things that sell your world to the players.
Keep in mind that, as a GM, you're a teller of stories. Like any movie director, novelist, playwright, or bard you're attempting to achieve a suspension of disbelief from those experiencing what you present. As such, study the arts. Remember the five parts of a story arc you were/are presented with in school? Intro, Rising Action, Climax, Falling Action, Conclusion? These aren't just topics to memorize for an english test. It's a time-tested technique to forming a story that WORKS.
When you watch a movie or read a book, watch how the author/director presents the world. Study the techniques they use to sell the action to the audience. There's loads of learning material for an aspiring GM surrounding you every day. Learn to notice it, and then learn from it.
Finally, don't script your players. Unlike actors in a movie, or characters in a book, they're not yours. Don't try to force them to become so. And, even more importantly, don't become discouraged when you can't tell the story you want.
Remember, the story revolves around the characters, and through them, the players. That doesn't mean you should make them the center of all creation, but you should tailor what happens to suit their own view of the world.
Remember, in an RPG nothing has meaning except in relation to the PCs. Think about this fact. Don't forget about it.
Let the world breathe. Let it, and the story within it, flow naturally. When you've truly reached that point, GMing is tiring, but the easiest thing in the world, because it all comes naturally, as if you're merely a channel for the world that exists in your mind. It should take on a life of its own, and make it's own decisions. When you become nothing more than a tool by which the world is envisioned, then you've gotten it right. And your players will love you for it.
2) How exactly do you DM a good session?
In the same way that the game world only exists in relation to the PCs, the way you GM should be based on the players, and the way they view the world. Try to cater to your players interests, but at the same time, keep pushing them to become more than they are. Challenge them!
When I say challenge them, I'm not talking in relation to the difficulty of the scenario, though that is iimportant too.
Sculpt things to make your players think. Put their characters in situations that make them question themselves.
Example: I was running a fantasy cyberpunk GURPS game where the players were cops in chicago in the year 2114. A werewolf was murdering people in their downtown apartments. Now, normally this would be a simple matter of lock-and-load-the-silver.
I didn't want that. It's too easy for them to just go into kill-mode and wipe out the menace. What's more, it's too easy on the players. They're used to thinking according to those lines. It becomes routine.
So, instead I decided the werewolf was, normally, a 12 year old at a local orphanage, who had severe mental issues.
When the players discovered this, and I made sure they would BEFORE they encounted the beast, the expression on their faces was priceless. Killing a slavering beast is one thing. Knowing that it's a young girl you're pointing your silver-loaded boomstick at is something completely different.
My whole point is that to make a session good, you have to snare your players. Get things going using stuff you know they'll jump in to (like an murder investigation that looks like it'll turn into a kill fest, always popular among my players) and then throw them for a loop. Make them question their own means.
When you get them to question, you get them to think. And when you get them to think, you've captured them into your world.
3) Would you recommend using a module at first, just to get used to DMing?
I suggest READING a few. They're great for learning how to put a good story together.
Just don't use them as a crutch.
Develop your own style. Don't ever run anything out of the box. Modules are generally written for an assumed 'ordinary' player. Adjust or re-write every module you use for who is going to be playing (the players AND the characters), and for your own GMing style (which you hopefully will develop as you gain more experience).
Most modules, when run straight, are awfully dry. Make it your own, and tune it for the audience.
4) If the players are more experienced than myself, will that matter?
Depends on the style of game being run, and the style of the players. Hostile, rules intensive, demanding players are a nightmare for beginning (and even experienced) GMs. If you have these, drag at least one aside and co-opt them into playing on your side. Find the one who's best at (and enjoys) keeping secrets, and give them a PC that is almost an NPC. You'll put the party on an internal leash, and it falls to that player to make sure the game runs smoothly, regardless of your level of experience, because you're letting that player play something so cool!
Creative, inspirational, and self-driven experienced players, on the other hand, are a joy to work with. Just give them a world to play in, a few leads, and some toys to play with and they'll write the story themselves, with little help from you, regardless of your level of experience. If you have these, just make sure you don't stifle them. Work with them, rather than against them.
5) What's the hardest/most time-consuming/disliked aspect of DMing?
Running a zillion NPCs all at the same time, in the same scene. Good NPCs have their own style, motivations, and tactics. When you have a bunch of these together all at once, and having to deal with a bunch of players vying for your attention, you can wind up with one WHOPPER of a headache really fast. It can also literally drive you nuts trying to stay inside the head of multiple different NPCs at the same time.
Oh, and playing two NPCs talking to each other, with the players listening, can be really tough to do right. Try to avoid this situation at all costs.
6) And finally, How did your first DMing experience turn out?
Well, since I was 11, it went quite well. The players killed a bunch of critters, looted the place, and were eager to buy new weapons and armor so they could kill more stuff.
I don't recommend this as an example, though.
and so the players trust me. But then, I have really cool players.
