How to get my dog to stop barking?

Okay, So I know that a lot of dogs bark because they're playful and thats how they show that they want to play, and I know that some are just raised that way, But my dog is protective of us, he wasn't raised badly or half-heartedly, he's a good dog, but when people try to approach me or my family members he barks at them, no matter who they are, he doesn't bite, he wouldn't harm them unless they were truely harming us, But he barks, a lot. I don't want to make him think that its BAD to protect us, It's a good thing, But I want to know how to get him to be MILDER with his protection of us, rather than barking mindlessly at any guests we have. He's also a min pin, in case that helps.