Summarize the purpose and rules of the contest. (Keep it simple.) The contest should require people coming to your place of business to enter.
1234, Main Street
Boston, MA 02123
08 April, 2005
<Recipient Address Goes Here>
On your next visit to <place of business> make sure you enter our <name of contest>. During <duration of contest> we will be taking entries to win <prize>.
<Reason for contest.> Don't miss this great opportunity.
See you soon!
encl: <List of enclosed items goes here>