The best way and almost the only way, is to find the most reputable agency to represent you. In the majority of the campaigns, of well known fragrances anyway, the models they use are popular. Many fragrances even contract celebrities for their fragrance campaigns. Amateur models are usually not selected as body size is not a factor and with the competition that exist in fragrance advertising, the companies must appeal to the masses who are used to seeing famous or popular people in the fragrance ads. The smaller percentage who are not famous per say usually have campaign contracts with the label who also has a fashion line such as Dolce & Gabana, Chanel, and Gucci. But even those models did not come from small agencies or craigslist. So the best way to become a fragrance model is to find an agency which has A-list clients in the fashion industry and try for the runway shows in New York, Paris, and Milan. Chances are, if you are not walking the shows you will not get the huge campaigns. Most of those who are in the campaigns have walked for the designer previous to said campaign. An example is Cara Deleveigne who walked for Burberry prior to a Burberry Fashion campaign and it was not until later after becoming popular that she appeared for Burberry fragrance.