There is a 2e accessory book called the Worldbuilder's Guidebook, that has a chapter on mythology and history. It suggests going through the initial myths, such as:
- Creation myths - How the world was created, what made it form and shape, etc
- Divine myths - What gods are there? Were there gods that came before?
- Sagas - Who are the historical heroes? What did they do to become heroes?
- Natural disasters - Were there any earth shaking changes? Meteors, volcanoes?
After that, it starts breaking it down into history, such as far reaching cataclysmic conflicts (WW I, II), longstanding kingdoms that either fell or not (Rome), and things of that nature. It also gives random tables to determine events, and ways to structure the timeline.
On a more modern note, if you have read through the Terry Brooks pantheon of novels, they are all really centered on Earth, and it's morphing from magic to technology and back again, might be worth reading through various synopses if you aren't familiar with the series.
One of the things that I found was asking myself questions about why a certain event may or may not occur really helped. Such as, if you have magic, why would you invent a technological solution? Well, because magic is failing there. Why is magic failing there? Because of XYZ? Why XYZ? and so on. This worked when I was detailing a world history for a campaign a while back.