"Startup growth breaks down into two components: The first is getting lots of users, ideally by creating a viral product."

"The second piece is keeping those users, also known as “retention”."

"Highly retentive products often draw in the user with variable rewards."

"1. Human interaction"

"Enable open-ended conversations and interactions between users. Notify users of incoming interactions, thus creating variable rewards."

"Once you’ve clicked on it, you get the relief of knowing what it is, along with the dopamine hit that comes from variable rewards you are presented with."

"2. Turn-based Structure"

"Establish a pattern in your app where one person is expected to act first, followed by an action of the second user. The first user is notified of the second’s move and brought back into the product."

"3. Scheduled Shows"

"Provide a regular, real-time show at pre-set time intervals. Notify users when the show is about to start, and let them know at the end of the show when the next one will happen."

"4. Status or Badges"

"The product rewards the user by upgrading their status or granting badges. Obtaining higher status can unlock additional features."

"5. Surprise & Delight"

"Upon completion of certain actions, users are rewarded with a pretty or funny clip or image which celebrates their work."

"6. Memberships / Subscription"

"Offer a membership subscription that provides clear time or money savings if repeatedly used. Users will keep returning for the savings you provide, and the sunk cost of having paid for the membership."

"7. Personalized Notifications"

"Provide relevant notifications to users based on what you know about them. Good targeting differentiates this from spam. This type of notification can work best for marketplace products."

"8. Share Improvements"

"Inform users about new features they may be able to benefit from. This is a high-cost strategy because you’ll have to keep building new features."

"9. Drip Marketing"

"Send new users a pre-scheduled set of emails or notifications informing them about the features of your product or promotions going on."

"Drip marketing informs your user about the product they just bought or signed up for, and encourages them to keep using it."

"Yet, it’s obvious to users that the emails are automated, and may feel a bit like you are sending them the user manual in chunks, so be careful as this can easily border on ‘spammy’."

"10. Incentives"

"Provide a discount or store credit which users can use if they return to your product. Works best for e-commerce products, but beware that it may cheapen your brand."

"11. Spam"

"The best, cheapest and most organic way to capture users is via genuine recommendations."

"Work out how you can incorporate variable rewards that bring so much joy to your users that they want to share your product with the world."

"If not applicable, then at the very least come up with some engaging communication strategies that don’t make them resent your brand, or a cool promotion that keeps them coming back for more."

"1. Two-Sided Reward"

"Create an incentive for a user to invite their friends, and for their friends to accept the invite."

"The above is also a nice example of the gifting effect."

"2. Appeal to Vanity"

"Appeal to users’ sense of vanity and competitiveness to encourage them to spend more time using your product and invite others into it. Expose metrics for them to drive up."

"In the early days, LinkedIn had a similar thing going. By showing the number of connections front and center on your profile, they incentivized you to start thinking about inviting more users to connect with you."

"3. Collaboration"

"Apps built for collaboration or communication between coworkers are inherently viral."

"4. Embeds"

"Create the ability for others to embed your product into their website."

"5. Artifacts Shared on Social"

"If your product creates uniquely interesting content, users can be encouraged to share it on their social networks, thus spreading knowledge of your product to their network"

"Pinterest would let you pin items from the web, and then share the pins onto Facebook. This worked really well."

"When someone discovered the Pin, they would click into Pinterest and be shown a collection of more interesting items, quickly going down a Wikipedia-style browsing black hole."

"Another way to draw attention to your product is watermarking: If your product creates images or videos of some kind, add a watermark into the main image to let users know where they were created."

"6. Artifacts Shared via Messaging"

"Your product generates artifacts or URLs that are expected to be shared via messaging."

"7. Signatures"

"8. First Message sent on Existing Messaging Platform"

"9. Highly Visible Hardware"

"Hardware products can be viral too. Think about Square:"

"Another very different example in the high visibility hardware category is the outdoor Nest Cam."