Identify the reader's need, propose your solution, tell them why your solution is the best and then give them an incentive to respond.
1234, Main Street
Boston, MA 02123
08 April, 2005
<Recipient Address Goes Here>
I understand that <need to be filled>. Very often you don't have the time to look for someone who can really help you. Or perhaps you think that extra service will cost you more.
At Abc Company, our customers' needs determine how we run our business. We pride ourselves in superior <products/service> and are always looking for ways to better serve you. <Merits of your products/service>
We'd like you to give us a try. If you stop in and bring this letter with you, we'll be happy to <incentive>. We look forward to meeting you and proving that Abc Company stands behind its promises.
encl: <List of enclosed items goes here>