[Help] - Dog barks at absolutely everything, where to start with training?

Hey all,So I have a little 4 1/2 year old Jack Russel/Rat Terrier mix named Snots. She is spayed and has very little obedience training due to living with my parents for 4 years - they're quite old fashioned and live on a farm, so Snots never had to walk on a leash or listen to commands. We are working on the leash training and obedience which is going quite well. She is extremely food motivated but easily distracted.The biggest issue is the barking. For some reason my dad got a kick out of riling her up whenever anyone knocked on the door or rang the doorbell, so she barks absolutely crazily whenever she hears anything like this, and continues for about 5 minutes between barking and "wuffing".I grew up with dogs, but am admittedly not great with training. I've read that positive reinforcement is key, but she just loses her mind every time she hears a sound that triggers the barking and there is nothing there to reinforce. Where do I start? I've been practicing knocking softly on tables and giving her a treat if she stays quiet, but jumping to the doorbell is proving a challenge. She doesn't even notice the food when she is barking. I'm not sure how to make her realize that if she is quiet, she'll get her reward. Obligatory dog taxAny help is appreciated! via /r/dogs http://ift.tt/2qTULZ5