One of these new features is called Instant Tuning, which allows you to quickly adjust the future behavior of app notifications whenever they appear in the Lock Screen or the Notifications Center. Here's how to make the most of it.
How to Use Instant Tuning in iOS 12
Next time an alert appears in your device's Notifications Center or on the Lock Screen, swipe left on it, then tap Manage. Alternatively, if your device supports 3D Touch, hard press on the alert and then tap the three dots in the upper right corner of the expanded notification.
A Manage Notifications pop-up will appear on the screen featuring two blue button options. Deliver Quietly ensures future alerts from this app only appear in the Notification Center (accessed by swiping down from the top of your device's screen).
Note that selecting this option means alerts will no longer show in the Lock Screen and you won't see any banner notifications on any other screens. Deliver Quietly also turns off any sound or vibration alerts set for the associated app.
If you tap Deliver Quietly and then decide you'd rather not stick with the setting, open the Manage Notifications pop-up again in the same way and tap the Deliver Prominently button to reinstate the previous settings.
The second option, Turn Off..., completely disables all notifications for the related app. Tap this button and you will be prompted to confirm it's what you want.
Below the two large blue buttons is a less prominent Settings button that takes you to the individual app's various notification options, usually accessed via the main Settings app.
From here you can adjust where alerts should appear (if at all), enable or disable sounds and badges, select alert preview options (Always, When Unlocked, Never) and choose how notifications should be grouped (Automatic, By App, Off).