First impressions: name, avatar and greeting
Small choices that change whether people talk to it at all.
The name
Name it after yourself. "Sarah's AI" or "Ask Sarah" works far better than "CoachBot" or "Assistant", because people came for you.
Be clear it is an AI. Naming it exactly your own name with nothing else leads to people believing they are messaging you.
The avatar
A photo of you beats an illustration or a robot icon. There are presets if you would rather not use a photo, but a real face gets more first messages.
The greeting
Two sentences. Say what it is, then name two or three things worth asking about. A blank "How can I help?" leaves people staring at an empty box.