Referrals are one of the highest-quality lead sources available to freelancers, a referred client arrives with built-in trust and typically negotiates less on price. Building a referral network deliberately, rather than hoping it happens organically, makes a real difference.
Start with existing happy clients. At the end of a successful project, it's reasonable to simply ask: "if you know anyone else who could use this, I'd appreciate the introduction." The testimonial request tool is a natural moment to add this ask.
Build relationships with adjacent freelancers who serve the same clients but don't compete with you directly, a web developer and a copywriter, or a wedding photographer and a wedding vendor, naturally refer work to each other. A simple referral agreement with a small referral fee formalizes this without making it awkward.
Keep a short list of people you'd refer work to and people who refer work to you, and check in with that list a few times a year, referral relationships fade fast without light, occasional maintenance.