Imagine this scenario: You, a veteran mountain climber, are slated to give a speech about climbing safety to a group of mountaineers that is about to set off on a dangerous expedition. What would be the best source of credibility in that situation? Experience! The mountaineers would probably not be very impressed to hear that you read a book about climbing safety once, or that some of your best friends are mountaineers.
However, if you bring in stories, photographs, and examples from your own climbing experience, you will assure them that you really know what you're talking about. Drawing from your work experience, volunteering experience, hobbies, and informally, other types of personal experience can do a lot to boost your credibility as a speaker.
Do you have any formal or informal training that relates to your topic? If so, mention it during your speech to build your credibility.
Relevant training programs and credentials include academic degrees, professional certifications, classes, conferences, and personal research.
Even if your training isn't directly related to your topic, there may be an indirect connection. Don't feel obligated to stretch your story if it really doesn't fit, but also don't rule out training experiences that are out of your current field.
The first method for estimating the intelligence of a ruler is to look at the men he has around him. —Niccolo Machiavelli
Machiavelli's maxim teaches a valuable lesson: people will not only judge you on your own merits alone, but also on the merits of your associates.
This rule isn't only for rulers, it applies to public speakers too. If you want to be seen as a credible person, align yourself with other credible people. You can do this by citing testimonials from respected figures or mentioning personal recommendations that validate your expertise.
Another approach is to quote prominent figures in your field, demonstrating an awareness of the issues and conversations that are current trends in that field.
Source: Boundless. "Types and Elements of Credibility." Boundless Communications Boundless, 17 Mar. 2017. Retrieved 23 May. 2017 from https://www.boundless.com/communications/textbooks/boundless-communications-textbook/methods-of-persuasive-speaking-15/credibility-appeals-76/types-and-elements-of-credibility-296-409/