1. Throw all open applications off the top of the screen

NOTE: If the screen stays off or gestures don't work, skip to 3. Trigger a restart.

1. If an application fills the screen and isn't responding, tap the gesture area or flick up on it to go to Card view.
2. Throw the card off the top of the screen to close the application.
3. Throw any other open cards off the top of the screen.

Why this might help

An open application can hold on to so much memory that there isn't enough left for anything else. Closing applications frees it.