The mail list, the offer and the creative. The rule is 40/40/20. The mail list is responsible for 40% of the success of the campaign, the offer is responsible for 40% and the creative 20%. If you do not have the right audience, your offer is useless. Make sure you are "talking" to prospects that understand the offer and will see value in it. If you do not have the right offer, the audience is not going to matter. Audience and offer are directly dependent on each other. If you are selling lawn maintenance services or invisible fencing, make sure you are talking to people who live in single family homes, and hopefully own them; not apartment renters. The 20% creative is the art; make sure it is attractive, noticeable and easy to understand.