1. Try Updating Again

If you’re still using one of the early versions of iOS 12 (or the beta), the first thing you should do is check for updates in 3uTools. Or go to Settings -> General -> Software Update and update to the latest available software.

Downgrading iOS is another choice, you can downgrade to iOS 11.4.1 as Apple still signing for it.

2. Check Your Battery Health

If your battery itself is damaged on unhealthy, it can slow down your phone, or cause it to crash repeatedly. Go to Settings -> Battery -> Battery Health. If the battery health is below 80%, you need to go to the nearest service station to get the battery replaced. Apple will replace the battery at a low cost until the end of 2018. 

3. Reduce Motion

iOS 12 has a bunch of new animations. And for some users, they can feel slower, especially on a new device like the iPhone X. Try disabling animations to see if it makes a difference for you.

Go to Settings -> General -> Accessibility and turn on Reduce Motion.

4. Free Up Storage Space

That old adage is still true. If your iPhone or iPad has run out of space, it will start behaving weirdly. Random slowdowns are one of the things that might happen as a result. Go to Settings -> General -> iPhone Storage to see a breakdown of how exactly your device is using up the available storage. 

5. Disable Background App Refresh

Go to Settings -> General -> Background App Refresh and turn off the toggle next to the apps you want to disable background data for. 

6. Reset Your iOS Device

This is the last and final option. If nothing you did above worked, it’s best to erase all data of the iPhone or iPad and to begin again. First of all, take a full encrypted backup using 3uTools.