Using this simple method for list building, you should see exponential growth within a short time of implementing it, and therefore your business could go viral to people interested in your services or products.
Create a newsletter list - MailChimp can be free for up to 2,000 subscribers.
Create a subscription form for the list.
Promote your newsletter signup list by mentioning a free weekly giveaway.
Once a week, host a Facebook live on your Facebook page for your business.
As a bonus, if you're a local business, allow the winner to draw for the next week's prize on the Facebook live session at your business's location.
Encourage those watching the Facebook live session to sign up for your newsletter.
Be sure to deliver the prize and hold the drawing weekly/monthly.
Reasons for this method:
You can email those subscribers deals and more.
You gain traction.
Facebook prioritizes Facebook live videos (so you're using Facebook's algorithm to help promote you).
It can be practically free to promote your business this way.