It is easier and harder to be funny than you think. Comedy is telling the truth in an original and (hopefully) artful way. This is true of any medium for expression.
Create an unique perspective and style that builds on predecessors with insight and wit to dissect a subject. Any subject is appropriate, but it must be something that tugs at your soul so deeply that you feel it in the pit of your stomach.
We laugh when there is a fact of life that is far too painful to take seriously. Allowing yourself to tell jokes about something people are uncomfortable with brings a taboo subject out into the open. In this way stress is relieved, by laughing at the realities of life.