It should help people connect to your friend. Keep your language simple and honest. People shouldn't have to concentrate to hard on what you are saying. It should flow more like a good tale rather than a lecture. Consider the folksy winsomeness of Charles Kuralt or Garrison Keillor.
People naturally resonate with a narrative style of speaking.
You don't want the eulogy to be a stand-up comic routine, nor do you want it to be a time of intense sorrow, but laughter and tears are perfectly normal and acceptable when you remember someone. A far as the format goes, tell a story or two from your own experience. Listen to the stories others tell and feel free to use them. These stories show that he did make a difference. Maybe he wasn't known as a great inventor or a great statesman.