There is no better way than to improvise and talk for example about experiences - personal or things you've read/heard from other people. If you don't really know, just think up something (listeners don't really know if you are lying or not, and they won't ask questions about every single thing).
However, what you really need to do is sound condfident, like you really know what you're talking about and you are prepared. Confidence is the key - as long as you look confident and don't stop talking, people won't question the credibility of your information that much.