iOS 11.4.1 is a mainly a security update, which means you should install it as soon as possible.
Please Backup Your iPhone and iPad Before Updating to iOS 12
Please make sure you have an iCloud and iTunes backup of all the devices you are planning to update to iOS 12 today (the update should drop in a few hours). This will save you data loss and frustration, should anything bad happen.
You can find a guide on how to do this here, on Apple’s support page.