We have been lucky enough to work with a number of retailers recently and the research and campaign results have given us a start to a growing library of marketing 'rules of thumb' that are proven to get the tills ringing.

A summary is below, but if you are interested in the details behind these learnings, please feel free to ask here, or directly through email, twitter etc...
Learnings
Retail Loyalty Marketing - 5 lessons learned at the till