To tell a funny joke, find a style of comedy or delivery that suits your personality, use content that make you laugh and deliver jokes that are appropriate for the audience to whom you are speaking. When delivering the joke, deliver the punchline clearly.
Identifying a specific style of delivery gives you a unique comedic voice. Some types of delivery include slapstick, situational, political, cynical or raunchy. Take a cue from your favorite comedians to discover what kind of comedy it is towards which you gravitate. Try similar methods of those styles to find one that fits.
Once a style is discovered, it is easier to choose a type of content. Some types of content include self-deprecation, current events, passions, annoyances and politically correct or incorrect subjects. If it makes you genuinely laugh, you are likely to deliver a joke in a more organic and funny manner.
A joke truly works when it is delivered to the right audience. For example, a joke that only adults might understand is not appropriate to tell to children, and vice versa. Use your whole body when delivering a joke, from your posture and body language to your voice and facial expressions. Only deliver jokes that you know well and consider truly funny.