Designing for the web is not like designing for paper. For one thing, paper-based designs tend to stay the same shape and size. Also the content doesn't obstinately change on you. In fact, very little learned in print design is applicable to the web.
Paradoxically, one of the best ways to embrace the dynamic, interactive nature of web applications is to start working with paper again. Paper not for printing or sketching, but for building functional, interactive prototypes; prototypes that do away with distracting high fidelity and embrace the messy process of creating fun user experiences.