I can't necessarily speak from experience, but from a marketing perspective, I would suggest a couple things:
(1) Remain consistent and develop a pipeline for each scenario. Pipeline for those who do not respond (send a second letter, maybe a third letter); pipeline for those who respond (offer a follow-up letter after a period of time if it doesn't work)l pipeline for those who respond and are interested
(2) Use a letterhead, if possible, to give it a professional feel and connection
(3) Place yourself in the shoes of the customer and ask yourself what the customer would want to know. Are you providing enough features, advantages, and benefits to the potential client.
Again, these are just suggestions, however, maybe some of this advice may help out some. Good luck on your second batch.
