extreme newbie turbo question

Hey i just bought my first turbocharged car, a 98 Audi A4 1.8T Quattro. I've always driven muscle cars, mainly mustang 5.0's, and at the moment don't really have a clue about turbo's. The german guy i bought it from upgraded the turbo when he orderd it from the factory(i gota check through the receipts he gave me to figure out which turbo is on there) and he said it's running at about 12-13 lbs. of boost. I want to get it up to around 18-20 lbs. of boost. My question is how do i get more boost out of the turbo without buying a whole new turbo. My plans were to get a boost controller and upgrade the DV. Anything else i can do and any suggestions on the best types of parts to buy would be greatly appreciated. (i should have what kind of turbo is in the car posted by tomorrow)