Agency owners: How did you find your first business development partner?

I'm a software developer with 5+ years of experience and I'm building my own software agency. I enjoy building products but not sales.

I'm exploring ways to grow—whether through referral partners, marketing agencies, or freelance business development professionals.

For those who run agencies:

• How did you find your first sales partner?
• What worked?
• What would you avoid?

I'd love to learn from your experience.