Start with an outline. For me, an example would be...
Three things that define me.
1. Dance
a. dancing all the time
b. hanging out with dance friends.
2. Family
a. movie nights
b. cooking dinner together.
3. Art
a. drawing all the time
b. art classes.
Once you have put together a similar outline, you need to practice speaking and expanding on these topics. Get comfortable with details and write suggestive notes if you forget. When speaking, glance at your outline if you get nervous. :) Hope it helps! :) and good luck on your speech! :)