Hi Sajan -

The introduction should be brief and accompanies by a really great (aka glossy and colorful) brochure and a website address where they can find/request more information.

The letter should briefly introduce your business and tell them why they should use (or need) your services (versus whoever they are using now). The brochure will really sell it because everyone will at least glance at a brochure.

Also, you should use a nice envelope - handwritten.

Also, you should be prepared to make several follow up phone calls.