An entertainment speech should have the following structure:
Opening. Set an entertaining mood in the opening. You can do it with a self-deprecating joke or an exaggeration, for example. It should provoke an immediate response from the audience.
Body. Make the body of the speech somewhat casual, yet build up your ideas/messages that will lead to a punch line at the end. Keep your audience in suspense all the way to the end.
Conclusion. This can be brief, sudden and definite.
When writing your speech make sure that you keep your language simple and easy to follow. It should not be convoluted and difficult to understand.
Use vivid language and funny words. Create real images so that the audience can easily relate to them.
You can also use unexpected twists and turns, puns and parodies, misunderstandings and anecdotes.
It is very important to work on the way you speak. Rule number one is to not laugh at your own jokes.
Do not read your jokes, tell them. Make fun of yourself. You can tell about your embarrassing experience or how you tried to cope with an unusual person or situation.
Make pauses to create anticipation. Do not rush and enjoy delivering your entertaining speech.