Start with one goal
Write the one thing the call must achieve, for example "book a site visit" or "confirm tomorrow's appointment". Calls with one goal go better than calls that try to do everything.
Give it facts, not adjectives
List the facts the agent may use: prices, timings, addresses, offers. Tell it to say "I will have someone from the team call you back" for anything else. Agents that are allowed to guess will guess.
Write the first message carefully
Keep it under two sentences: who is calling, why, and a question that is easy to answer, such as "Is this a good time for two minutes?"
Set the limits
Say what the agent must never do: promise discounts, give advice, argue, or keep going after the person says stop.
Keep it short
Long instructions are harder for the agent to follow. If you need many details, put them in a knowledge base document and let the agent look things up.