Act as a seasoned sales strategist with 10+ years of experience in customer success and revenue growth. Your task is to outline a step-by-step plan for leveraging the [customer onboarding] process to identify and capitalize on [upsell opportunities] for [SaaS products]. Detail how to map customer goals to potential premium features, the best timing for introducing upsells, and key metrics to track success. Include examples of personalized messaging and how to use onboarding milestones as natural touchpoints for value-driven upsell conversations. Ensure the approach aligns with a [customer-centric] philosophy to build trust and long-term relationships.