So you've decided to write about the end of the world. Good for you! Whether it's live blogging the cataclysmic events ("OMG! Here come the comets! UPDATE: I guess technically they're asteroids") or leaving behind a written document for the small bands of plucky, post-apocalyptic survivors to study as they're picked off one-by-one by zombies or the new dinosaurs, you're taking on a monumental task and should be applauded for doing so. Here are some helpful DOs and DON'Ts to assist you.
DO find a comfortable place to write - Your usual spot might not suit your needs. Near that one window where you set up a small antique desk because normally you can expect lots of natural sunlight to pour in so you can look out and see a pond while listening to birds chirp in the trees may not be the best place to put you in a writerly state of mind when people are running around, screaming in terror as the earth's crust cracks open, spewing forth hordes of lava demons. Try a large closet or in the bathtub.
DO try to adhere to your usual writing routine as much as possible - If your iPod has a certain playlist you enjoy listening to while you write, by all means, let it play. Sure, our existence is being snuffed out forever but you're not obligated to listen to "Ride of the Valkyries" or "O Fortuna" or Juice Newton if you don't want to.
DON'T be inconsiderate - If you get started and suddenly realize, "Oh snap! I'm out of coffee. I need to go to the store!", don't park in one of the accessible spaces because you figure it just doesn't matter anymore. That's a dick move. Respect the needs of others right up until the point that there aren't any more (needs or others). However, if you've always wanted to jump out of a moving vehicle and let it just crash into traffic and explode, I think people would understand that this is your last chance to do so and support your right to cross something cool off your bucket list. So I guess that would be DO commit futile, flamboyant last gestures but DON'T be inconsiderate.
DO take breaks as needed - We know what day the apocalypse is happening but we don't know how long it's supposed to take. It could be an all-day thing and you're going to get tired. Don't let that happen. You need to stay fresh! The worst thing that could possibly happen is if you look over your work when you think you're all finished and realize, "Damn it, I started three paragraphs in row with 'AUUGGHHH!!' I need to re-edit the whole thing!" Well, that won't be the worst thing, but you get the idea.
DON'T forget to spellcheck - The end of the world is no excuse to be careless and sloppy.