How do you ensure your color is correct for printing?

[FrameSmile]

As I typically work on the printing and manufacturing side of the business, I am wondering how you, as a professional photographer, ensure that your colors are perfect for printing?

What types of questions do you ask your print house?

Which type of color system(s) do you follow?

How do you adjust for extended color systems?

I'm just curious what different people do for their workflow.