You can customize Control Center in iOS 12, so you can quickly change the settings for the things you do the most. Here’s how:
Go to Settings > Control Center.
Tap Customize Controls.
To add controls, tap the “+” button. To remove controls, tap the “-“, then choose Remove.
Want to rearrange controls in Control Center? Just go to Settings > Control Center, tap Customize Controls, then touch and hold the three horizontal line icon next to the controls and drag them in the order that you want them.
(This how-to is based on my experiences and info on Apple's support pages — where the images sometimes come from.)