Fix Underbite First or Have Teeth Shaven?

I want to have my underbite fixed by a dentist and also have my teeth shaved down to fit the others in size. I thought about veneers but they are expensive but I do want to fix the appearance of my over all smile. I saw a dentist now and he fixed all my cavities and said, I should be happy with the way I look, but I'm not. Do you have any suggestions on what I should do first? Please help. Thanks.