A consultation works best when the stylist or beauty professional can see where you are now and understand where you want to get to. You do not need a polished brief.
Useful things to bring
Reference images, a rough idea of your normal routine, any known colour history, and honesty about how much time or maintenance you want to commit to.
What not to worry about
You do not need to know technical colour names, exact service terminology or the difference between every treatment on the menu. That is what the consultation is for.
Ask practical questions
How often will this need refreshing? What will the grow-out look like? What can I realistically recreate at home? Good answers to those questions are more useful than salon jargon.