Most marketing activities have to be done a few times before they start to make a positive impact on important things like sales. They also get better and better with a bit/a lot of testing and refining.

We'll start by pulling ideas together into a plan that'll get your newsletter launched and loved. 
We'll take the time to figure out what you customers (and aspiring customers) really want to receive in their e-postbox.  You know how we'll know? Email is the most amazing thing because it mails you back! Seriously. It sends back a whole bucket-load of really useful info. We'll know such things as:
Who loved the subject line so much they opened your newsletter immediately.

So, we'll plan and test and improve and plan and test and improve and so on and on.
We'll work towards a goal we'll set with you at the beginning and gauge each newsletter's progress against it, so we all know we are doing a good job (because that is the point!).