Pinterest Reached Entire Communities By Targeting Community Leaders

A typical product might see 90% refuse to sign up to a product. And then of the ones who do sign up, over 90% of users disengage and become inactive over time. These metrics are terrible, but they’re normal.
Mobile apps often have better engagement metrics, but have lower upfront conversion rates. SEO products have the lowest signup rates.

4 steps to create a delightful onboarding experience -
1) Identify your product's value to users
2) Map out the user's journey toward experiencing that value.
3) Identify the obstacles along the way.
4) Address those obstacles using your onboarding experience.
Twitter studied their users' onboarding behavior and discovered that if a new user doesn’t follow at least a handful of other Twitter users immediately upon signing up, they’re much less likely to return in the near future.
Get more from user observations:
As a result, Twitter redesigned their onboarding flow to force users to choose five people to follow. They showed celebrities you're likely familiar with based on the topics (e.g. sports) you indicated you're interested in at the start of onboarding.