The iPhone and iPod touch can't easily change the brightness of the screen without opening the Settings app. This tweak creates a simple way to change the brightness: with the volume buttons.
Simply activate the Activator action (set to pressing both volume buttons by default) and the volume controls will then change the brightness instead. Activate the action again or wait 30 seconds and the buttons will control volume again
Credit to @HellFireAE for the idea.
Configure Activator from Settings