Secure an internship in the fashion industry. Even if the position doesn't give you as much creative control and responsibility as you'd like, you'll earn experience in the inner workings of the creative and business process and make professional contacts.
Develop a complete portfolio of designs as well as actual samples. This includes patterns, sketches, photographs and prototypes of your original designs.
Present your clothing at fashion shows and "fashion week" events in different cities. While you probably won't, as a novice, be able to break into a catwalk event in Milan Fashion Week, you can contact the organizers of smaller, local events to have your pieces shown and, hopefully, be noticed by a fashion buyer.
Make contacts with the buyers at local clothing stores and boutiques, especially smaller ones that may be more open to unproven designers. Schedule meetings to present your designs and prototypes and convince them to sell your clothing at their stores.
Market your designs independently by building a website, using social networking tools, blogging, tweets, etc. The more you market your ideas, the more likely an interested buyer or retailer will be interested.