One of my favorite speakers, Tim Gard is one the funniest speakers I know. If you ever get a chance to hear him speak ... don't hesitate! The best part of his humor is that he is "relate-able." Tim's humor evolves from his personal experiences - which likely mirror many of YOUR experiences. What I remember about his advice to being funny is that a) you should never make someone other than yourself to butt of the joke and b) if ANY of your material is offensive to a member of the audience, ditch as quick as you can.
Let's face it, life should be fun! As you remember the funny experiences in your life, write them down and feel free to work those stories into your speech. Not every single detail, just the parts that help someone realize why it's funny. The shorter the better. Actually, I believe most people like their humor like they prefer their candy - smooth and sweet.