Before you tell someone about HIV first, try and find out what the person actually knows already about the virus. You could start up a conversation about something you read or saw on the TV or online. See what they say and how they react.
If they say things about HIV that you know aren't true and you feel comfortable, you can correct them, stating references that are in the public domain, such as an organisation or website.
You could bring HIV up with them a few times so you get a good idea of what they know and feel about HIV. You can also use this to educate them, so they now know the facts before they know anything else.