A speech is nothing but a way of telling the world what you are burning inside to tell.
Before you write a speech you need to ask yourself:
What is that one thing that you have been keeping inside you that you would want to share with the world?
Have you had an experience that has changed you as a person and can be an inspiration to others?
Once you have an answer to these questions start writing what comes to your mind. Don't worry about the structure, the beginning, the conclusion. Just focus on penning down your thoughts. Once you have penned down your thoughts now its time to add a good opening statement and a good concluding statement or thought.
That's it. Your speech is ready. It's probably still RAW but it's a speech. And remember the golden rule in speech writing - “A good speech is never written, its always rewritten”.