Effective user onboarding utilizes a combination of email, in-app messaging, and product tours. Emails are useful for delivering transactional messages and longer-form content designed to re-engage users. In-app messaging is ideal for important announcements and critical product changes relevant to active users. Product tours help highlight the value of features and nudge users towards key steps in using a product. SaaS tools like MailChimp, Outbound.io, Intercom, and Chameleon can be used to design, build, implement, test, and iterate on these channels. It's crucial to measure success with a single metric that everyone is committed to.