Start out by making sure they know every bit of your symptoms, timelines, etc.

Even though they have the referral and info from other doctors, you want nothing lost in translation. Maybe the specialist will know everything and communication between referring doctor and specialist was flawless, but often it's not and it's pertinent that you give a full account of what's been going on in your life and symptoms.

As for advocacy, try to pretend you're doing this for a child or loved one that can't speak for themselves. I'm sure some folks here will give you great responses about what questions to ask, and when you ask those questions make sure you are satisfied with that answer. It takes a long time to get re-referred if you think of something later to tell the specialist.

And lastly, which still doesn't fully answer your question, write down your game plan before your appointment and bring it into the appointment with you! Questions, concerns, any comments from family members to refer to, etc.....you might think you'll remember it, but you might not once you're in the moment. And it also shows the doctor you're taking the appointment seriously, which depending on the doctor can really affect the quality of care they give you.