Beyond being visible and easily located, it’s also really important that you sell the sign-up! Simple requests like “sign up for email” or “sign-up for our newsletter” don’t really tell me much about what I’m getting, why I should care and how often I’ll be receiving mail. 

For best results, explain the benefits of signing up and set expectations: 

• mention frequency explain what will be sent 
• link to an example newsletter or email 
• if possible consider offering an incentive (coupon/contest entrance) with sign-up

Read the full article: Optimize Your Email Sign-Up Part 1: Stand Out & Entice.