There is no quick and easy way to identify a winning formula. The proof, as is so often said, is in the pudding. This means, the only way to discover what marketing medium/copy/material really works, is by testing it.
Direct marketing, unlike most other forms of marketing, can be subjected to accurate testing. Whether you’re sending email shots, posting out brochures or phoning your prospects, the results of your campaign can easily be recorded and analysed.