How do you get money from a client who won't pay?

I'm curious to know, how do you effectively retrieve funds from a client who has refused to pay? Have you encountered this situation before, and if so, what strategies have you employed to overcome this obstacle? Are there specific legal channels or negotiation tactics that you've found particularly effective in such scenarios? Understanding the best practices for collecting outstanding payments can be crucial in maintaining a healthy financial portfolio, so I'm eager to learn more about your approach.