1. Make sure you're offering the type of content that will attract the people you want to target.
2. Figure out: What do you want these people to do? What's your goal? Sign up for your newsletter list? And if that's the immediate goal, what's the end goal? More revenue? Paying customers?
3. How can you entice customers into signing up -- what can you offer beyond your awesome content? Maybe an ebook freebie? A webinar? These types of incentives will drastically increase your sign-up rate.
4. As someone else here mentioned, pop-ups work. We use Pippity or LeadPages on a few blogs and see conversion between 4-7%.

Good luck!