How to tell a joke or not?

I am absolutely sh*t at telling jokes.  Firstly, I can never remember jokes when I want to, if I do remember them I often start giggling part way through but worst of all I often forget the punchline which can be hugely annoying.

It looks like this may be hereditary.  We’ve been trying to expand Madame’s repertoire of jokes, beyond ‘what do you call a goat with pants on it’s head?’ which there is no punchline but results in fits of laughter from her.

How hard can it be to tell a Knock-Knock Joke?