Never apologize to an audience before you speak. Never say things like: “I am nervous about public speaking” or “I am new at this topic. So please bear with me.”
Let’s face it: If you are truly nervous, the audience will soon find out. So telling them beforehand is nto going to help you.
The irony is that very often we feel a lot more nervous inside than it is shown outside. Even the best speakers feel a bit nervous before speaking but they don;t show it. Likewise, your audience may not even know that you are nervous. So why confess? Remember: We are often the harshest judge of our own performance.
When you apologize at the outset by saying that you are new at the topic, you are telling your audience to expect a bad presentation. You are telling your audience not to listen to you. In fact, you are destroying your own credibility before you have a chance to demonstrate you have it. This is like going to battle and telling your enemy that you are weak and asking him to slaughter you. Does not make any sense at all.
There are more practical tips in my book.