Here are some guidelines to make your unsubscribe process as easy as possible for those that want out:

• Include the unsubscribe link at the top of the email – don’t bury it in the footer where it might be missed. If people can’t find the unsubscribe link, they’ll use the Report Spam button instead
• Implement a single click unsubscribe process instead of requiring subscribers to enter their email addresses
• Include a way for subscribers to opt-in to your lists again in case they accidently removed themselves from your list
• Set up a valid email address subscribers can reply to in order to unsubscribe from your list and monitor it closely.
• Remember that your opt-out mechanism must be able to process requests for at least 30 days after the message was deployed
• Always always always use a suppression list

Source: Listrak’s white paper Increase ROI with List Management Tactics