Some of the best places to have the “STD talk” is after dinner when the check has been paid, in a dog park while watching pooches going at it doggie style, or after a friendly bowling match. It gives you both the freedom to leave if the conversation becomes uncomfortable.
Your attitude will convey how you feel about yourself and your date; don't sound apologetic or anxious. You can even practice what you're going to say beforehand so that you feel more confident.
Try something like this:
“I care about you and like being with you, so before we fool around, I want to tell you what I've been tested for and share my results. I do have the human papillomavirus, as well as herpes. Both are treatable and there are means of having safer sex. I want you to feel free to ask me any questions and I'd also like to know what you've been tested for.”
Respect their emotions but don't tolerate any disrespect to you personally.