What post-sale strategies have you found most effective in driving customer success and retention?

The most important part is actually having a post-sales strategy. A solid plan.

In today's market space of 'delivery-by-tomorrow' the focus is highly targeted at execution of the sale. Very little is dedicated to 'genuine' post-sales client engagement. Digital polls, email feedback requests, etc simply to not engage in real value. Asking for a simple five star review does not create client trust and is not a strategy to the clients benefit. In today's world of digital communication overload, the best post sales strategy is a Person-to-Person, Voice of the customer. We like to target these at 3, 30 and 90 days post sale, and annually touch base.   

Leveraging work management platforms like Asana, and feed data into your CRM or customer success platform.