-First, create the universe.
-Second, check your materials. If you’ve got a proper universe you should have a lot of hydrogen right away, which you’ll need if you want to have stellar bodies and such instead of a distorted groaning trainwreck. For tips on crossing this crucial threshold, see pages 8-12: Baking A Bigger Bang.
-Third, stir repeatedly. You want continual expansion.
-Fourth, pick a star, any star. If you’re an expert try for one that isn’t going to burn itself out in the next few billion years but most of us aren’t and if you choose wrong you’ve lost nothing but time so who cares about that anyways.
-Fifth, find a planet near your star and prepare to get some kind of complex garbage in a self-replicating mood. Prod the atmosphere with whatever materials you have to hand in the rest of the solar system and just keep dropping rocks on it until you see something that looks sort of but not entirely like rock diarrhea. That’s the miracle of life.
-Sixth, wait.
-Seventh, wait some more.
-Eighth, keep waiting. What you’re looking for is life to get just complicated enough to be capable of stellar observation and stupid decisions. If your life seems to be stuck for more than a hundred million years or so, try dropping more rocks on it and seeing what happens. Again, time is not your limiting factor here.
-Ninth, make sure your life doesn’t invent light pollution before it invents astronomy. This happens more often than you’d think and it always makes you feel like a complete putz.
-Tenth, watch as they figure out how the sky seems to work. They’ll likely alternate between being dead on and totally and incomprehensibly incorrect, savour this while it lasts.
-Eleventh, cross your fingers. You’re hoping for a calendar that doesn’t run back to front or have a month inserted inside another month or get decided purely by whenever’s the best time to have elections but even those rejects can sort themselves out if you wait a few thousand years (see: Rome; Earth – Sol system).
-Twelfth, get ahold of a lot of something fermented and just barely this side of toxic. You want to feel like your ass is in orbit without removing your liver all at once.
-Thirteen, party down. Hoot, holler, eat whatever passes for food, make bad decisions and rash promises! You’ve successfully brewed up your very own New Year’s! Now that you’ve created one of the simpler holidays, why not try your hand at whipping up something more complex and unrelated to astronomical phenomena, like some kind of parade* or national holiday**?
*Only applies if your lifeforms are capable of marching in a somewhat straight line; nobody likes a zigzaggy parade.
**First see pages 7890-7891: How to Create Nationalism, and be sure to only do this in an open and well-aired space: nation-states explode easily when they feel threatened.