Tomorrow I have a meeting with a lingerie company and I got the meeting by looking in WWD in the Classified section. I notice brands and get the contact information and ask if they need a model. I send a nice photo that matching the type of modeling job I am trying to get. ( I send a nice scam of my body compcard that showed my legs and body.) The biggest thing when approaching brands is to ask for the person who makes marketing and model decisions. And to not be afraid to take a chance for yourself.
Same goes for any brand or product, most companies have websites and most brands wll at least direct you or lead you to the right person and then you can send a nice photo.
PHOTOS are a big thing, if you are sending your photos ANYWHERE, to an agent, to a brand, to a magazine you should make yourself look as honest as what you really look like, you should be sending photos that represent the style of the brand. You shouldn't dwell too much on it, but you should be picky about what you send, because first impression is important.
For a petite girl, I would say: the more commercial, the more energy and the more personality you show in your photos the better. To get modeling work as a petite model it involves having more personality than pouty lips and the same pose sometimes.