I do the same thing that Ashley mentioned for barking.

I have two under-socialized dogs. And let me tell you, it is NOT fun trying to socialize them as an adult. Kai was our first dog so what I assumed was enough socialization wasn't even close to enough. I didn't expose him enough to cars, crowds of people, water, and a whole bunch of other stuff. So now, it makes walking extremely difficult. I'm convinced Kaedyn wasn't socialized enough towards (mainly) people and also dogs. He has a dominancy problem and doesn't trust people at all. Anyways, just try doing as much socializing as you can. It makes everything SO much better when they're adults. Take him everywhere you can. Around busy areas, crowds of people (I took Kai to parades and dog get togethers for that), around buses, bikes, skateboarders... everywhere you can get to!