How do you get a dog to stop barking?

Barking at the door, at people. It gets worse and of course its not a pleasant thing. He's rebellious, but not even too old yet, but he's already picked up the habit of barking A LOT to certain family members for nothing, and sometimes me and siblings if he doesn't get what he wants including attention after we stay away from him for being so loud and bad. :/ suggestions please?