If you want to take a portrait, tell them what you like about their outfit, a certain look or something else. Most people just want to know why are you doing this kind of stuff and what is it for.
And the most important thing is to be honest to others and yourself. Try to enrich your life by learning from others. Listen to other people and their stories. This will maybe inspire you to take more photographs in a different way or about a special topic. And you can give away a free smile to someone else making their day a bit brighter and better.
Be kind to other people. Because you are not alone.
You are part of a world wide community of photographers.