Generally, you should address two topics: safely in a normal situation and emergency safety.
First, you should tell them how to behave on the boat, for example what kind of behaviour could lead the boat to capsize and that they shouldn't drink alcohol.
Second, you should inform them what to do in the case of an emergency. For example, you can tell them where the live vests are and how to attract attention while in water (with a whistle attached to the live vest).
