Famous wedding dress designers like Vera Wang or Priscilla of Boston had to start somewhere. Create your dress design niche by finding individual or personal inspiration to apply to your creations. If you have the time and dedication to hone your craft, you may someday see your designs walk down the runway.
Go to school for fashion design. This is not absolutely required, but a quality design school will teach you the building blocks for the design and creation of a wedding dress. While in school, you can also make important contacts in the fashion field, or find possible internships at wedding dress design companies.
Design your own dresses while in school. Find inspiration in nature, art, people and places. Create dresses based on the personalities of people you know. When you have a portfolio of your best works, send them to design studios, along with a resume highlighting your schooling and any experience you have.
Find a paying design job, or look for non-paying internships at design companies. Many of the best designers start at the bottom, and you can compile important knowledge while working your way up in the company.