Idea: Gain new subscribers/customers by offering double-sided rewards to referrers.
Details: Having your customers refer your product can greatly lower your acquisition costs, but you need to make sure that your offer is enticing enough for your customer to refer. For instance, I don't really have the desire to refer a product unless my friend and I both receive a reward, because I'm not going to refer unless I receive a reward, and my friend probably won't sign up unless he/she receives an award.
Your reward does not have to be costly; just offer a nice discount or free shipping to both parties. For example, Airbnb allows you to send your friend a $25 coupon, and once they use it, you also get $25 off your next stay. It's a win-win all around!