1. Provide a "Join my list" form on your website and blog.
In this day and age, website traffic and blog traffic are incredibly high intent. Make it easy enough for interested visitors to join your list with popups and website widgets to collect email addresses.
2. Turn social media followers into email subscribers with landing pages.
Relationships on facebook, Twitter and other social networks are great, but with the constant algorithm changes, it's far more valuable to own your relationships than hope to reach those people on the social networks. Posting landing pages focused on email subscriptions, and perhaps, offering incentives for them to join your list, is an easy, free way to get more subscribers.
3. Ask in-store customers or booth visitors to subscribe to your list.
Do you regularly attend events? Do customers walk through your store every day? Consider using an iPad app, or even an old fashioned pad of paper to collect more email addresses on the go.
4. Add opt-in capability when customers register for events, or send ideas, comments, requests.
This is another easy way to encourage those who are engaging with your business to subscribe to your email list. If someone is registering for an event you're running or filling out your contact form on your website, adding an opt-in check mark is a great way to capture their interest
5. Run small offers that explicitly ask for email subscription in exchange.
To really accelerate email acquisition, providing a stimulus can really incentivize someone to join. Think "Register for our newsletter, get a bag of chips on your next visit". It's amazing what offers can do to grow your email list!