What strategies can you use to quickly learn about the needs of your customers?

Found this and decided to bring it here. Imagine you're in charge of a product that needs to grow or die in the next 30 days. What strategies can you use to quickly learn about the needs of your customers? Let me know your thoughts and tips. Also if one of your tips is to talk to customers or do research, here’s a mind blowing product discovery tool for you (https://www.producthunt.com/prod...)