there are many ways to go about goth clothing, but mine is to buy just some plain staple pieces (black jeans, black shirts, black skirts or dresses, leather jackets, etc), and then really jazz up your outfit with accessories. whether they be pins and patches on a jacket, or more gothic jewelry, anything really goes.
i don't know if this really helps, but maybe you can get a general idea of what i was trying to get across.. lol.