In this article, Simms Jenkins share a couple of questions to ask yourself to ensure you treat your email sign-up form/preference center like a binding contract:

What did you say you do?
Offer up the benefits and a general overview of what they would be receiving.

Can you show me what you are talking about?
Samples can help seal the subscription deal or alleviate any fears of potential subscribers that they may just be receiving “a bunch of emails” with little value.

How often will we be talking?
Spell out how often a subscriber will receive your emails. Don’t mislead users.

What’s in it for me?
An enticing reward can often help create the email relationship and convert many would-be email subscribers.

May I make a suggestion?
Let your new email subscribers choose some content and have some control over their subscription, whether it is HTML vs. text, the frequency, the language or just a nice menu of newsletter and email offerings.

How well do you want to get to know me?
The general rule is that with more than four to five fields of information you may start to lose potential subscribers. If you are not using the information for segmenting, than just ask for a first name and email address.

Why should I trust you?
Make your privacy policy accessible for your future subscribers with just a simple link.

How easy is it for me?
Ensure your sign up form can be found (and completed for most) on the home page.

Can you please confirm that with me?
Tying in with the incentive aspect, your confirmation email/page is a great spot to receive the actual coupon/white paper and engage the new subscriber right away.

Source: iMedia Connection