The official route requires you to be signed up for the Apple Developer Program so you can get it today; the public beta will arrive later this month. If you can’t wait, you can try Apple blogger Sam Henri’s method.
Naturally, you’ll want to proceed with caution and back up your data before trying this out. It’s also worth noting that the beta can be unstable, is prone to crashing, and doesn’t yet include all the features revealed at WWDC.
Still up to the task? Here’s how to do it:
You’ll need to fire up this page (samhenri.com/ios12) in Safari on your iOS device, and then click on the teal colored button labeled ‘Download iOS 12’ at the bottom of the page. That’ll set you on the path to installing a profile and rebooting your device.
Once you’re done with that, you’ll need to head into Settings to initiate a software update, and when it’s finished, you’ll have iOS 12 running on your iPhone or iPad.
Our own Nino de Vries gave it a go and managed to get iOS 12 up and running on his iPhone X in roughly 10 minutes; hopefully, you’ll have a similar speedy experience. Here’s a list of all the devices that the new version is compatible with: