If you have a 3D Touch-enabled device (iPhone 6s and newer) it’s possible to use the display’s pressure sensing capabilities to quickly change apps. The app switcher view is usually opened by double-tapping the Home Button, but this is an even quicker alternative option. You can also launch the app switcher by swiping right from the left-hand edge of the display while pressing hard on the screen.

Alternatively you can swap immediately to the last opened app if you drag all the way from the left to the right edge of the screen. You can very quickly move between two apps in this way – great if you’re taking notes or referring back and forth between two documents!