The coaching certification you earned provided you with a coaching process. The quality of your coaching process and the services you provide leads to referrals. This will happen naturally in that satisfied clients will send other people. It is also smart to be proactive and ask your clients for referrals. Plan ahead for ways to approach it, what you want to offer, and the timing of your request for referrals.
For example, because the Code of Ethics calls for full disclosure of compensation for referrals a great win/win is to offer both the referring client and the new client the same benefit. Some coaches give a free session, others provide a gift card, or be creative and offer a special resource that has value for your clients.
As a coach it is important to let your clients know that you want and appreciate referrals whether or not you offer something for the referrals. Make it easy for your clients. As one example, invite your existing coaching clients to give their contacts a free introductory session with you for coaching so they are comfortable making the referral.
Be ready when your clients thank you for how you helped them or when they share their successes and follow-up with an email or note asking them to help others they know utilize the coaching too. Provide a link to information about how coaching will benefit them, your coach training and related experience, and how they can easily schedule an initial session.
When your coaching services make a difference they want to share it with others and by making it easy for them to refer people they win, their contact wins, and you win too.