|Garde Manger Guy|
Even if you want to craft your own world and test your universe making skills the advice remains the same. Start small.
Steven King gave an interview once about how he built his most recent novel at the time. (Storm of the century)He noted that the idea came to him of a man in a jail cell. Then he hit on the idea of the sheriff and his deputies being terrified of this man that they had in the cell. After that the entire town was fearful of this man. Why were they? How did it happen? A small start to a larger story.
You don't need the complete backstory to Lord of the Rings, Game of Thrones, or The Wheel of Time at your first session. You will need a reason for four to six first level characters to meet up and adventure together. Saving the multiverse can come later.
With first time players it may take multiple sessions for you and your crew to decide on what characters they are most interested in playing/running and what location they are most interested in playing in. (Water based, forest, cityscape, etc.) I would run several loosely connected scenarios with each one of those themes to get a sense of what your group (and you) like best. Keep the stuff you like and focus on that.
Remind everyone that mistakes will happen and that everyone is there to have fun.
Once you have them hooked after a month or so you then let them know that if they bring you food and wash your car every week that "the gods will be merciful". It may take a few sessions for everyone to decide what is fun for them. Enjoy getting them there.