well, as a new mc myself (ive only run three sessions so far, and its my first gming experience ever), here's the approach I've taken to apocalypse world so far:
1. come up with a core concept first, i.e. zombie apocalypse, nuclear winter a la fallout, or simply a general theme you want your apocalypse to embody.
2. after world creation and character creation, look for where the PCs aren't in control: when you get the actual book and stuff, there's literally a move for the MC that's "look for where they're not in control, push there" there's also "respond with fuckery". by that it means, push where the PCs have no control and watch them try to figure it out. i know it sounds sadistic, but trust me. this step is more of a general rule to follow throughout play.
3.build off of what your players give you: this means watching their actions and moves and come up with ways to reward or screw with them about it, and then reward if they pass your screwing with them. Other times though, it can simply mean an inadvertent action creating a whole new plot line. For example, my brainer came into the session, rolled weird to get info on a certain infection that was taking the town, got his information, then stone-cold executed the poor sons of bitches to stop the infection. I had no intention on any of that happening, but then was able to build off of that into an interesting story. I really should've done more with it than i did, but it was only second session.
4.Also, again in the MC rulebook, there's a thing that says "after every action ask: what do you do?" This one is huge. I have literally planned the bare minimum for my sessions and they've all wound up great. Why? Because of this rule right here. The awesome thing about AW is that the story-building happens around not just what the MC decides to throw at them, but also what the players wind up doing with themselves. That story up there occured because of "what do you do?" I've realized I'm a very improvy GM so, for me, i plan the bare minimum, but the point here is to be flexible and if you get a sudden burst of creativity, go with it! It creates awesome stories.
The thing about Apocalypse World is it's a snowball-y kind of game. I.e. this roll leads to this which leads to this etc. So, always always always be building off of something, even if it's something you just happen to pull out of your hat.
Seeing as your players are new too, I also suggest this: first, be patient with them. Second, let them try and figure out what their character would do in this situation, and make sure it's their character; and part two to that is ask them questions about their character, even if it's the most minute things, but also try and get at their emotions. "What are you afraid of?" "What does x mean to you?" "What would you be willing to trade anything for?" Things like that, and then give them time to answer. It's about asking provocative questions, and I wish I had the link on me that gave some really cool examples. This process allows them to flesh out the character so you have even more stories to build from! Cause you can totally, absolutely, one hundred percent take something from a character's backstory, file it away for later, then drop it like a bomb a few sessions in.
This is a lot of information, and I kinda suck at explaining things, so I'll just stop here for right now.