1. Start on your website and blog
Most websites have hidden, embedded forms somewhere deep on their site. That's really not enough. Turn on website banners or popups and use targeting like timed auto show or exit intent to really turn things up on your list growth efforts.
2. Leverage Social Media
Just because someone is a fan of your page on Facebook, doesn't mean they're also subscribed to your newsletter. Post frequently to your Facebook page, Google+, Twitter and any other social channels with landing pages pointing people to subscribe to your newsletter.
3. Use your Email signature
Over the course of a week, hundreds or thousands of people are likely reading emails you send out. Adding a landing page link to subscribe to your newsletter is a great way to point additional, high intent audience to subscribe to your email list.
4. Ask People in-person
If you regularly attend events to market your business at trade shows and have a booth, put out an ipad that lets people subscribe to your email list as well. Same goes for in-store customers if you run a local business.
5. Find Partners that can help grow your audience
See if any friendly partners of yours would be willing to post an offer to their social media audience or in their own newsletter. That will help increase your audience with new leads and potential customers who might be interested in what you offer and have not yet seen you before.
The above tactics will absolutely help you begin to grow your list. Make sure you have the basics in place with a standard "join my list campaign" and if you want to accelerate your email list growth, you can turn things up with offer driven campaigns instead.