Just use a form of the verb "to be" in front of the expression.
ex. I am not long for this world.
ex. She's not long for this world.
That's one of my mother's favorite expressions. She usually says, "I'm not long for this world." immediately after watching the 10pm news. It just means that she's tired.
You can also use it to refer to someone who is dying. "He's not long for this world."
hope that helps
