How do I set minimum purchase requirements for discount codes?

I'm struggling to create discount codes that only apply when a customer's cart reaches a certain total value. My current approach of offering blanket discounts is hurting my profit margins, and I want to encourage larger purchases while preventing small, unprofitable transactions. I need a strategic way to set minimum purchase requirements that motivate customers to add more items to their cart without creating too much friction in the buying process. What are the best practices for implementing minimum purchase thresholds for discount codes?