Best Gemini AI call structure

Hi,
I’m looking for the best API call structure for Gemini to set the SYSTEM prompt only once and not in every request.

Want to extract specific data from a job offer like min./max. salary, working experience, an do on.

For this, I want to set up the AI once (manually or via API) and send the different job descriptions one by one afterward.

What is the best approach to archive that?

I’m new to AI and Gemini so maybe someone can give me some hints.

Technically, I already set up the API calls with cURL and stored the prompt in data types.

Thanks,
Gerald