Have a Simple and Prominent Unsubscribe Link

Don't bury your unsubscribe link at the top of your email messages. Contrary to belief, put the unsubscribe link at the top of your email. This will broker trust with your email recipients and prevent them from hitting the spam button. If recipients grow frustrated by not being able to find the unsubscribe link they'll take the easy route and click the spam button. The goal of email marketing is quality, not quantity.
Make the unsubscribe process easier than the subscribe process.