I am starting a clothing design company (women's clothing), and targeting the boutique owner/stores/online places to sell my merchandise. I want to send them an introductory letter with my catalog. I want to explain how much stuff is different and how it could work for their business. Can someone please suggest me something or start the letter. Thanks!

Your very first sentence should be the hook, a concise, one-sentence tagline. It could be or become your motto, should grab the reader's attention within a couple of seconds. That's all the time you have to get someone to read further. Your hook should immediately, instantaneously open the reader's eyes, grab his attention, and get him thinking about how you can add to his bottom line.

What is unique or interesting about your products? How could adding your products improve their sales?

I agree with WG that first comment could also be a question pertaining to a situation or problem common to your industry.

Then present a quick resolution in your next sentence.

Stringer