One of the things you will find as you GM is that one of the keys to success is finding your own style and one that meshes well with your players, so take all the advice you get in this thread with a grain of salt. We can tell you what works for us and our group, but not necessarily yours. That said, what can I suggest?

Worldbuilding:
Be clear on what your group wants. If they are all new to the game and the system, they may not know what they want, so you might want to try some different approaches, or even just sit around for a while and discuss it amongst yourselves. Some players really enjoy the tactical elements of DnD, especially as it has so many mechanics and related techniques and possibilities for leveling, comboing, etc. I've played with groups who see the "talking" parts of the game as mere bridges between epic, hour long combats, which is what they enjoy. Others, such as myself and my playgroup, enjoy the roleplaying and storytelling aspects of the game far more, to the point where we have abondoned DnD for other, more rules light systems, where tasks and combats can be resolved faster and more simply.

It seems like from what you're said that you, as an aspiring writer, and your group, with no previous experience, are likely more interested in the creation of a story than the application of tactical, blow-by-blow fights and magical abilites. Now, I'm a biased source as I abandoned DnD a long time ago, but I've always found that its basic structure (not that you can't make fantastic adventures that don't adhere to that) revolves around going on scripted missions with liberal amounts of level-balanced combat (your typical "dungeon-crawl", if you will), and many pre-gen adventures you get will have that as an underlying formula. If you find your group enjoys that, great, you should have lots to start from and work with, but if your group found the level 1 slog of fighting Kobolds for no reason other than they were there, and livened up when you added story, I imagine that they will be invested in richer worldbuilding than that.

Now, there's two types of larger story you can use to involve your players. One is a linear narrative you construct before hand (the typical "man approaches you with a quest"), and the other is a more open and reactive world. Both have their benefits and difficulties. A linear plot you craft, much like a story plot, can be well thought out before you ever play, which means you will have prepared what comes next for your players long before they encounter it. You will always have something for them to do, and for new players who often seem lost, it gives them a clear sense of purpose and something to strive towards. If it's thought out to give everyone some motivation for participating in the quest, and there are challenges for everyone to overcome, each player gets to feel like they contributed something and got something out of the adventure.
However, there are drawbacks. Once, not when, your players go "off the rails", you can find yourself at a loss, with hours of carefully scripted adventure thrown out the window, and if you are not good at improvisation, things can grind to a halt. If the players don't feel invested in the story, or feel they can't contribute, or decide they would rather do something else, they can get frustrated and create tension. And the plot does come across quite clearly as something you have constructed for them to embark on, which can sometimes lead to the feeling that they are merely doing what you've already decided for them to do.

The other option is to attempt to craft a wider world, with independant characters with personal motivations and goals and schedules. Dropping players into a world where they are free to interact with anyone and attempt to do anything can be very exciting for your players, and give them the sense that they are truly controlling their own characters. However, it can also be overwhelming for new players hoping for a sense of direction and purpose. If you want to go this route, instead of coming up with one story, create 3-4 characters with motivations that don't rely entirely on the players (a villian with his own plans, a noble who is trying to stop him, a crook with plans to take over the underworld, a farmboy with plans to kill his parent's murderer, a plot to overthrow the monarch, etc.), and perhaps a handful of ideas for quests if you need them (Farmer Edric got kidnapped by Orcs, there's something spooky being seen in the graveyard at night, the brewmaster needs a new shipment of barley that hasn't come, etc.). You can roughly frame out what your characters will be doing to one another over time, just as you might lay out the plot for a novel. Then drop your players in the middle and let them go. If they have no inclination and no direction, you have plot hooks ready to go ("help, help, won't anyone save my uncle?", a beggar stops you and asks you if you're here for the prince's tournament, someone warns you not to stay in that in, people keep going missing from it, etc.). If they find something interesting, or have a character story they want to pursue, let them go about it, and every so often update them on what else is happening around town. If you have an evil necromancer trying to raise an army of the dead and a nobleman trying to field a party of heros to stop him, don't drop that story just because the players declined his offer. Mention the parade given to the adventurers that are setting out to face a great evil, make note that the bartender's sister is looking after the inn while he's away, maybe even have them encounter a great battle as they're travelling across the land.

Worldbuilding like this is less work than it seems, as all you have to do is brainstorm half a dozen single sentence ideas, as I did above, and think each of them through only a little. If your players follow up on one of them, you can plot it out more, but the rest can remain just ideas in the background, making the world seem much bigger, but without really taking that much work. However, if you do this, best to make it clear to your players that they don't have to do everything you mention, otherwise they might think that they're expected to follow up on each and every plot hook. If they expect to be fed a story in this manner, you might be better off just coming up with a quest for them, as above.

Character Creation:
When I start a new adventure, I sit all my players down together during character creation and ask them what they want to do. There's no sense in investing time and thought into a plot that they will get bored of or refuse to follow through on. If they lack ideas, I brainstorm with them, telling them what ideas I've had and seeing if they like them. Furthermore, I always make a point of tying the story I'm going to make in to their character's stories. If Bob rolls up a high-charisma rogue and starts playing right away, what's he going to do when you ask him for his action? What does he want to do? What does his character want? If all he has to go on is the knowledge that he's a rogue, the possibilities are endless, and he has no way of knowing what he wants.
"I go and steal something, I guess?"
But if Bob wants to roll up a rogue, and you start asking the group questions about their characters, "Who are you? What do you want out of life? What do you like, what do you hate?", he can start to have some idea of who he is. Even if he can't spontaniously create a wholly formed character, he can write down what few things come into his head.
"I...am looking for the man who killed my father. I'm a brilliant swordsman, I like pie, and I hate mimes."
If your players have clear character ideas, great, they get to tell you them. If not, you get something halting and awkward like that, but if you make them write it down anyway, it gives them something to work from. It can always change later when they get a better idea of who they are. At least now, when you ask Bob what he wants to do, he can say:
"I go and ask if anyone has seen a six-fingered man. And I buy some pie."

Equally important is to understand why the swashbuckling rogue, the Cleric who won't tell anyone who he worships and always carries a spatula, the Dwarf with a compulsive gambling problem and a kleptomanical Druid whos animal companion keeps leaving droppings everywhere are all travelling together. Because if there are any personality conflicts (and there will be), they need some reason to not just go their seperate ways. Before you start plotting an adventure, make everyone tell you something their character wants to accomplish, and talk about what you could all be doing and why you'd be doing it together. If you all just want to meet for the first time in an inn so you can take a quest from a hooded figure, that's fine, but talk with your players and at least get an "okay, fine, whatever, I don't know." before they start bickering and trying to kill each other.

You should find that even if the players don't have a clear idea on what they want to do, they can come up with a rough idea in broad strokes, and may even be able to play off each other to craft a description of the adventure they want. If they got together to agree on an adventure, they should be much more invested in following through on it, even if it's as simple as "You like treasure? I love treasure! You know what has treasure? A dragon! We should totally all go and kill a dragon, and then keep its treasure! That would be cool!"
I have never regretted getting my player's input on what kind of adventure they wanted, and on weaving their character's motivations into the story.


Whew! So, that's what I'd suggest before you get started. I'm going to do another post on other topics, as this got kinda long.